Symposium on the Chemistry of Natural Products, symposium papers
Online ISSN : 2433-1856
Search
OR
Browse
Search
Current issue
Showing 1-50 articles out of 104 articles from the selected issue
  • Tsukasa Hirokane, Yasuaki Hirata, Takayuki Ishimoto, Kentaro Nishii, H ...
    Pages Oral1-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Ellagitannins are a structurally and biologically diverse class of hydrolysable tannins. In ellagitannins, nearly 40% of characterized natural products possess the “digalloyl structures connected by C–O” such as dehydrodigalloyl (DHDG), valoneoyl, and tergalloyl group. These motifs cause the production of dimeric and oligomeric ellagitannins to be a main factor of the structural diversity. In this study, we describe a novel method for synthesizing the digalloyl structures connected by C–O including DHDG, tergalloyl, and valoneoyl group, along with investigations intended to synthesize cornusiin G, a dimeric ellagitannin.

    The synthesis of this work commenced with construction of the DHDG group, which was composed of the three steps sequence including the oxa-Michael addition of phenolic nucleophiles to 13, successive elimination, and reductive aromatization of o-quinone monoketal. The method could be applied for the syntheses of valoneoyl and tergalloyl groups by changing the nucleophile to 10 or 11, respectively. Therefore, o-quinone monoketal 13 is concluded to be the unified synthon for synthesizing the digalloyl structures connected by C–O. This method of synthesis would expand the synthetically available ellagitannins.

    View full abstract
  • Akane Hirose, Takanori Murakami, Masaru Hashimoto
    Pages Oral10-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Lambertella corni-maris invades Monilinia fructigena on Apple fruits. This phenomenon so called mycoparasirism can be reproduced on Petridish as a fungal replacement without competitive inhibition. We have disclosed that diffusible and inactive lambertellols A (1) and B (2)1 are transform into active form lambertellin (3).2 Since the acidity by the host Monilinia stabilizes 1 and 2, these can defuse to the area where the host inhabiting.3 However, we did not understand why the parasite needed to acquire such a complicated mechanism. We recently revealed the mechanism named “lambertellin system” which can rationally and fully explan the phenominon. Lambertellin 3 is toxic against both the host and parasite. The parasite detoxifies it by biodegradation. The “lambertellin system“ constantly works regardless to the exsitence of the host Monilinia fructigena. Mass spectrometry using 13C labeled 34 was effective to prove that. Cultivation with labeled 3enabled us to assign the GC peak of the degradation product, because this showed a characteristic molecular ion due to isotopomers. This peak was also detected in the regular cultuture broth, but showing simple molecular ion.

    Probably the parasite Lambertella could not acquire the substance which is toxic specifically against the host, because Lambertella and Monirinia are genetically close (Sclerotiniaceae). In the symposium, the details will be introduced.

    References

    1) T. Murakami, M. Hashimoto et al.T., Org. Lett. 6, 157 (2004).

    2) M. Nomiya, M. Hashimoto et al., J. Org. Chem., 73, 5039 (2008).

    3) T. Murakami, M. Hashimoto et al., Biosci. Biotechnol. Biochem., 71, 1280 (2007).

    4) T. Murakami, M. Hashimoto et al.T., J, Am. Chem. Soc., 126,9214 (2004).

    View full abstract
  • Yu Nakagawa, Takashi Doi, Takara Taketani, Kiyonori Takegoshi, Yasuhir ...
    Pages Oral11-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Pradimicin A (PRM-A) and its congeners are the only family of non-peptidic natural products having a lectin-like property to recognize D-mannose (Man) in the presence of Ca2+ion. Coupled with their unique Man binding ability, they exhibit antifungal and anti-HIV activities through binding to Man-containing glycans of pathogens. Notwithstanding the great potential of PRMs as the lectin mimics and therapeutic leads, their molecular basis of Man recognition has yet to be established. Their aggregate-forming propensity has impeded conventional interaction analysis in solution, and the analytical difficulty is exacerbated by the existence of two Man binding sites in PRMs and the formation of multiple complexes with Ca2+ ion and Man. In this work, we investigated the geometry of the primary Man binding of PRM-A by the recently developed analytical strategy using the solid aggregate composed of the 1:1 complex of PRM-A and Man. Evaluation of intermolecular distances by solid-state NMR spectroscopy revealed that the C2–C4 region of Man is in close contact with the primary binding site of PRM-A while the C1 and C6 positions of Man are relatively distant. The binding geometry was further validated by co-precipitation and isothermal titration calorimetry (ITC) experiments using deoxy-Man derivatives, leading to the finding that PRM-A binds not only to terminal Man residues at the non-reducing end of glycans but also to internal 6-substituted Man residues. The present study provides a crucial step toward an understanding of how the non-peptidic small molecule recognizes Man and Man-containing glycans.

    View full abstract
  • Shigeru Matsuoka, Shigeru Sugiyama, Daisuke Matsuoka, Mika Hirose, May ...
    Pages Oral12-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Our research interests focus on the lipid-protein and/or lipid-lipid interactions, which are predominantly controlled in a non-directional manner; van der Waals forces, as well as electrostatic and water-molecule mediating interactions, play important roles there. Particularly, mechanism of molecular recognition in the hydrophobic region of lipid membranes is in high demand not only for protein science but also for natural products chemistry to gain a better understanding of molecular mechanism of bioactive compounds that target lipid membranes and membrane proteins. However, the estimation of the total effects of multiple non-directional interactions is far more difficult as compared to the effects of highly directional hydrogen bonds usually occurring in drug-target interactions.

    In this study, we examined the molecular mechanism in the structure recognition of fatty acid by human fatty acid binding protein 3 (FABP3), by means of combination of thermodynamic and structural biological methods. Fatty acid is one of the simplest lipid molecules, and FABP3 is a small cytoplasmic protein (15 kDa) serving as a carrier of fatty acids.

    A unified interaction analysis between fatty acids and FABP3 was implemented by isothermal titration calorimetry (ITC) using fatty acids bound to liposomes. The results showed that FABP3 possesses relatively high and similar affinity (Kd= ~1 mM) to fatty acids with a chain length of C10-C18. The analysis of thermodynamic parameters indicated FABP3-fatty acid interaction is enthalpy-driven.

    The co-crystal structures of FABP3-fatty acids were obtained for C10:0-C18:0 at extremely high resolution by using SPring8 beam lines. The results showed that an additional network of ordered water molecules was found in the binding pocket of co-crystal with a C10:0 ligand to be forming hydrogen bonds with hydrophilic residues of FABP3. These water molecules were substituted by alkyl chains of longer fatty acids in C12:0-C18:0 co-crystals. These observations indicate that the water molecules in the new hydrogen bond network are involved in the retention of the similar binding affinity to C10-C18 fatty acids. Substitution of water molecules on a hydrophilic protein surface by a lipid alkyl chain may be one of the important models of lipid-protein interaction, which may lead to a better understanding of the molecular interactions among diverse constituents in cell membranes.

    View full abstract
  • Masayoshi Arai, Takashi Kawachi, Chiaki Nakata, Naoyuki Kotoku, Motoma ...
    Pages Oral13-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    It is generally accepted that the cancer cells, which have adapted to hypoxic environment in tumor tissues, aggravate the pathology of cancer by promoting tumor growth, angiogenesis, metastasis and drug resistance. Therefore the compounds that selectively inhibit growth of cancer cells under hypoxic environment are expected to be new leads promising for molecular targeted anti-cancer drugs. So far, we have reported that furospinosulin-1 (1), a marine spongean furanosesterterpene, showed selective anti-proliferative activity under hypoxic condition. Compound 1 also exhibited anti-tumor activity by oral administration in a mouse model inoculated mouse sarcoma S180 cells. A mechanistic analysis revealed that 1 suppressed transcription of insulin-like growth factor (IGF)-2 gene, which is selectively induced under hypoxic condition, by inhibiting complex formation between nuclear protein and the oligonucleotide containing Sp1-like consensus sequence.

    In this paper, we proved that 1 showed anti-tumor activity via acting on the hypoxic region in tumor tissue as well as in vitro property of 1. Moreover, two transcriptional regulators, p54nrb and LEDGF were figured out as the binding protein of 1 by using the oligonucleotide probe containing Sp1-like consensus sequence and the furospinosulin-1 (1) probe, and we then clarified that hypoxia-selective growth inhibition was observed in both p54nrbgene-knockdown and LEDGFgene-knockdown DU145 cells.

    View full abstract
  • Nobuhiro Koyama, Yuriko Tokoura, Atsushi Fukumoto, Yong-Pil Kim, Atsuk ...
    Pages Oral14-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Our research group has focused on the discovery of new leads for combination chemotherapy against MRSA. A b-lactam drug imipenem clinically used in hospitals is inactive against MRSA. Microbial culture broths were screened for potentiators of imipenem activity against MRSA. In the course of this screening program, a new compound designated cyslabdan was isolated from the culture broth of “Streptomyces cyslabdanicus” K04-0144. From spectroscopic analyses including NMR, its structure was elucidated to be a labdan-type diterpene connecting to an N-acetylcysteine residue via thioether linkage. Among b-lactam drugs, cyslabdan effectively restored carbapenem activity against MRSA by 500 to 1000 fold, whereas had no such restoration activity with other typical antibiotics (streptomycin, vancomycin, tetracycline and ciprofloxacin). From study of the mechanism of action, cyslabdan was found to be bound to FemA, which is involved in the synthesis of pentaglycine interpeptide bridge of MRSA peptidoglycan. Furthermore, the results of peptidoglycan analysis of cyslabdan-treated MRSA and the effect of cyslabdan on FemA enzymatic activity also supported the conclusion that the primary molecular target of cyslabdan is FemA. Cyslabdan is demonstrated to be the first microbial product which inhibits MRSA FemA. The reason why cyslabdan can restore imipenem activity against MRSA is also discussed.

    View full abstract
  • Junko Ohkanda, Michiko Takahashi, Akie Kawamura, Chenyu Wang, Atsushi ...
    Pages Oral15-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    14-3-3 proteins play a critical role in serine/threonine kinase-dependent signaling pathways through protein-protein interactions with multiple phosphorylated ligands. A ligand-dependent 14-3-3 detection technique would facilitate elucidation of 14-3-3-related intracellular signaling networks. In this presentation, we describe phosphopeptide-dependent fluorescent labeling of 14-3-3zusing cell penetrating probes derived from a diterpene natural product, fusicoccin. In vitro evaluations demonstrated that these compounds site-specifically attached a fluorescent tag onto the protein surface as a result of the formation of ternary complex with the 14-3-3 protein and a phosphopeptide ligand. Screening a phosphopeptide library for the labeling reaction demonstrated that the fusicoccin-anchor in the probe precisely recognizes the structural difference of the residue at position i+1 in the phosphopeptide, thus enabling selective 14-3-3 labeling depending on the shape of the ligand. The BODIPY-attached probe 1b labeled human endogenous 14-3-3 in cancer cells under hyper-phosphorylation conditions, proving that 14-3-3 is a primary target of the fusicoccins in mammalian cells. This cell-penetrating labeling agent may provide a useful tool to explore the mechanism of antitumor activity associated with fusicoccin-related agents.

    View full abstract
  • Tsutsumi Hiroyuki, Sato Takashi, Kinoshita Yoshifumi, Mukaida Hironori ...
    Pages Oral16-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    When a hot tea beverage cools down, it becomes turbid and brown-white particles settle out. This phenomenon is called a “creaming” or “creaming down reaction”. Previously, Ina et al. reported that creaming down eventually occurs when an aqueous caffeine solution is poured into an aqueous EGCg solution. We therefore attempted to crystallize a crude precipitate formed by creaming, which was made from an aqueous solution of EGCg and caffeine. An aqueous solution of equimolecular amounts containing gallated catechin (-)-epigallocatechin-3-O-gallate (EGCg) and caffeine afforded a crude precipitate by creaming, which crystallized slowly for about three months at 10℃ to give a colorless block crystal. The crystal was determined to be a 2:2 complex of EGCg and caffeine by X-ray crystallographic analysis. The 2:2 complex was formed with the cooperative effect of three intermolecular interactions, π-π and CH-π interactions, and intermolecular hydrogen bonds. Upon formation of the 2:2 complex, a caffeine molecule was captured by a hydrophobic space formed by the aromatic rings A, B, and B’ rings of two EGCg molecules. It was therefore thought that the crude precipitate by creaming occurred from the aqueous solution of EGCg and caffeine due to its high hydrophobicity.

    To confirm the findings, stereochemical structure and intermolecular interaction of complex of EGCg and nicotinamide, which is also one of tea ingredients, were investigated. An aqueous solution containing equimolecular amounts of EGCg and nicotinamide afforded a 2:2 complex of EGCg and nicotinamide. Just like 2:2 complex of EGCg and caffeine, nicotinamide molecules were captured by a hydrophobic space formed by three aromatic rings, A, B, and B’ rings of EGCg in the 2:2 complex of EGCg and nicotinamide. It was considered that EGCg captured various heterocyclic compounds in its aromatic rings, A, B, and B’ rings in aqueous solution. Then the capturing ability of EGCg for various heterocyclic compounds has been investigated.

    View full abstract
  • Midori A. Arai, Naoki Ishikawa, Takashi Koyano, Kowithayakorn Thaworn, ...
    Pages Oral17-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Basic helix-loop-helix (bHLH) repressor- and activator-type transcription factors play essential roles in proliferation and differentiation of neural stem cells (NSCs). Hes1, one of bHLH repressor-type factors, suppresses transcriptions of bHLH activator-type factors such as Mash1 by binding to their promoter regions as homodimers, which leads NSCs to remaining undifferentiation. Therefore, inhibition of Hes1 dimer formation would accelerate NSCs differentiation into neurons and glial cells. To quickly find ligands of bHLH factors from natural products extracts, we constructed Hes1 immobilized sepharose beads-HPLC method. Flavonoid glycosides (1-3), xanthone derivative (4) and polyene macrololactam (5) were isolated rapidly by this method.

    Compound 1 disrupted Hes1 dimer formation in mouse embryo fibroblast cells (C3H10T1/2), and moreover, 1 suppressed Hes1-mediated repression of bHLH activator-type transcription factor dose-dependently (reporter assay). In differentiation of mouse neural stem cells (MEB5), neurite outgrowth enhancement by 1 was clearly observed. The expression of pro-neural genes (activator-type bHLH transcription genes) such as Mash1 and NeuroD were increased by treatment of MEB5 with 1compared with those of control. These results suggested that the inhibition of Hes1 dimer formation by 1 would greatly contribute its mode-of-action.

    Compound 4 inhibited Hes1-mediated suppression of gene expression in reporter assay, although Hes1 dimer inhibition was not detected. The mechanism of 4 would be different with that of 1.

    View full abstract
  • takahiro abe, natsuko shirakawa, kiyotaka akiyama, kenji miyamoto, yas ...
    Pages Oral18-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Many structurally unique compounds with significant biological activities have been isolated from various marine invertebrates. In particular, sponges (phylum Porifera) have been shown to be a source of many significant natural products.Halichondrin B, halichlorine, and halichonine were successfully isolated from the Japanese marine sponge Halichondria okadai. Recent studies have suggested that many marine sponges harbor microbial symbionts, actually produce bioactive compounds, and that the number of cultivable bacteria represents 1% or less of the total environmental bacteria. To efficiently take advantage of sponge symbionts, a metagenomic analysis is a promising culture-independent technique. We previously constructed a metagenomic library using a fosmid as a vector, and isolated a clone that produced pigment. We isolated the novel pigment halichrome A, which was determined to be a biindole, and which exhibited cytotoxicity against B16 melanoma cells. This result suggested that a metagenomic approach is an attractive for screening natural products. In this study, we developed a metagenomic approach by solving the following problems: i) Generally, a synthase of natural products, polyketide, and non-ribosomal peptide constitute a gene cluster. Therefore, we need a metagenomic library that can harbor whole gene clusters. ii) On the other hand, host cells, such as E. coli, cannot necessarily express metagenomic DNA. Therefore, transcription must be able to occur without depending on a promoter derived from a metagenome.

    The marine sponge H. okadai was crushed with buffer and separated by centrifugation to give pellets. The bacterial pellets were wrapped in an agarose-plug, digested by a restriction enzyme, and separated by pulsed field electrophoresis. Isolated genomic DNA was ligated into BAC vector, which can accommodate huge genomic DNA. Furthermore, we improved this BAC vector to transcribe the incorporated genome. We successively incorporated the T7 RNA polymerase gene into BAC vector. Finally, we constructed a modified BAC metagenomic library. Studies to identify bioactive compounds in this library are underway.

    View full abstract
  • Taishi Kusama, Naonobu Tanaka, Jun'ichi Kobayashi
    Pages Oral19-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Bromopyrrole alkaloids found in marine sponges have attracted widespread interest due to their fascinating chemical structures with high N to C ratio (~1:2) and intriguing biological activities. In our continuing search for structurally unique natural products from marine sponges, we studied for metabolites of an Okinawan marine sponge Agelas sp. (SS-162).

    The sponge was extracted with MeOH, and the extracts were partitioned successively with EtOAc, n-BuOH, and water. The EtOAc-soluble materials were partitioned between n-hexane and 10% MeOH aq. Repeated chromatographic separations of the 10% MeOH aq.-soluble materials gave nagelamides X-Z (1-3), while nagelamides U-W (4-6) were isolated from the n-BuOH-soluble materials. The structures of 1-6 were elucidated on the basis of spectroscopic evidences.

    Nagelamides X (1) and Y (2) are dimeric bromopyrrole alkaloids with a novel spiro-bonded tetrahydrobenzaminoimidazole and aminoimidazolidine moieties. Nagelamide Z (3) is the first dimeric bromopyrrole alkaloid involving the C-8 position in dimerization. Nagelamides U (4) and V (5) are the first example for bromopyrrole alkaloids possessing a g-lactam ring. Nagelamide W (6) is also the first monomeric bromopyrrole alkaloid having two aminoimidazole moieties in the molecule.

    In antimicrobial screening for nagelamides U (4), W (6), and X-Z (1-3), 1-4 and 6 exhibited antimicrobial activites against some bacteria and fungi. In particular, nagelamide Z (3) showed potent inhibitory activity ageinst Candida albicans (IC50, 0.25 mg/mL).

    View full abstract
  • Seiho Kikuchi, Shinnosuke Ezaki, Tomoyuki Koyama, Haruka Nokubo, Takes ...
    Pages Oral2-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    An azatricyclic alkaloid (–)-lepadiformine A (1) was isolated from the marine tunicate Clavelina lepadiformis Muller in the Mediterranean near Tunisia by Biard and co-workers in 1994 (Scheme 1).1 1 exhibits cytotoxicities against various tumor cells [IC50= 9.20 mg/mL (KB), 0.75 mg/mL (HT29), 3.10 mg/mL (P388), 6.30 mg/mL (doxorubicin-resistant), and 6.10 mg/mL (NSCLS-N6)] and also possesses antiarrhythmic and antihypertensive properties. The complex skeleton structure is characterized by the trans-1-azadecalin AB ring system fused with the AC spiro cyclic ring, four asymmetric centers including nitrogen-substituted stereogenic quaternary carbon, and the B ring as a boat form. Although the specific skeleton structure and the eminent biological activities have prompted many synthetic organic chemists to promote the total synthesis so far,2,3 we embarked on the total synthesis of (–)-1 based on our original synthetic methodology.

    The retrosynthetic analysis of (–)-1 is shown in Scheme 1. The key feature is construction of the AC spiro cyclic ring system 3 from acyclic enone substrate 4 by a novel Hg(OTf)2-catalyzed cycloisomerization reaction developed in our laboratory.5 Treatment of 4with 0.05 equiv of Hg(OTf)2 in MeCN at rt for 45 min afforded the desired AC ring system 3 as a single diastereomer in 74% yield (Scheme 2). Conversion of 3 into Kim’s intermediate 2resulted in the formal total synthesis of (–)-1.3e To modify the problem in the formal synthesis by Kim et al. (Scheme 3),2b we tried to carry out the key cycloisomerization reaction with a new substrate 13 bearing required all carbon atoms (Scheme 5). The Hg(OTf)2-catalyzed cycloisomerization reaction of 13diastereoselectively proceeded as well to give the AC spiro cyclic ring system 21 in 71% yield. The cycloisomerization product 21 was converted into (–)-lepadiformine A (1) via deoxygenation of the carbonyl group and the stereoselective B ring formation. Thus, we have accomplished the total synthesis of azatricyclic alkaloid (–)-lepadiformine A (1) utilizing our original Hg(OTf)2-catalyzed cycloisomerization reaction of 13 to 21 as a key step. This novel Hg(OTf)2-catalyzed cycloisomerization reaction could be useful for construction of complex natural products.

    View full abstract
  • Ryosuke Sugiyama, Shinichi Nishimura, Nobuaki Matsumori, Yuta Tsunemat ...
    Pages Oral20-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Cell membrane is one of the most challenging research subjects, partly because lipid functions at a molecular level are largely unknown. We are conducting chemical genetics approaches using compounds targeting lipids to elucidate the structure and function of cell membranes. Here we report that heronamides, polyene macrolactams from a marine-derived Streptomces sp., are a unique class of membrane binders.

    We have constructed a screening system to find natural products targeting membrane lipids, using fission yeast as a model organism. During the course of the screening, we isolated heronamides, polyene macrolactams from a marine-derived Streptomyces sp. NSU893. The chemical structures of heronamides including 8-deoxyheronamide C (8-dHC, 1), a new analog, were determined by chemical conversion and spectroscopic analysis. Among heronamides, 8-dHC (1) exhibited unique cell growth inhibition pattern that was typical for membrane binders. To demonstrate the affinity between heronamides and lipid membrane, we examined surface plasmon resonance (SPR) analysis. The sensorgrams indicated that 8-dHC (1) and heronamide C (2) strongly bound lipid membranes consisting of lipids with saturated acyl/alkyl chains. In microscopic analysis, drastic morphological changes were observed when fission yeast cells were exposed to heronamides. Interestingly, this phenomenon was critically similar to that reported for a mutant of sphingolipid metabolism. These results suggest that heronamides target cell membrane probably by binding to membrane lipids, such as sphingolipids.

    In conclusion, we isolated heronamides and revealed that they bound to lipid membranes consisting of saturated acyl/alkyl chains and caused a drastic morphological change in fission yeast cells. Detailed analysis of their modes of action is underway.

    View full abstract
  • Ken nunettsu Asaba, Masaya Harada, Masumi Iwai, Mee Wah Lo, Noriyuki K ...
    Pages Oral21-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Voacanga africana (Apocynaceae) is a tropical tree distributed in West Africa and used as traditional medicine. However, bioactive principles of this plant have not been clarified.

    In our continuous studies on the indole alkaloids, we isolated 9 bisindole alkaloids including 3 new alkaloids, and 19 monomer alkaloids including 7 new alkaloids from V. africana (root bark). All newly isolated bisindole alkaloids are Aspidosperma-Aspidosperma-type alkaloids. Voacandimine A (1)is a novel bisindole alkaloid, in which unit A and B are linked by a piperidine ring consisting of Na’, C-2’, C-16’, C-22’, C-14 and C-3 positions. This linkage mode was unveiled for the first time in Aspidosperma-Aspidosperma bisindole alka- loids. On the other hand, as monomer alkaloids, Iboga-type indole alkaloids are mainly isolated. Voacangalactone (11) is a new hexacyclic Iboga-type alkaloid with a lactone ring consisting of C-16, C-22, O, C-20 and C-21, and this is the first example of natural Iboga-type alkaloids with such a function. We found that some of the Iboga-type indole alkaloids showed cannabinoid CB1 receptor, transient receptor potential cation channel vanilloid type 1 (TRPV1) or transient receptor potential cation channel menthol type 8 (TRPM8) antagonistic activities. These are the first examples of natural alkaloids having such activities.

    Asymmetric total syntheses of Iboga-type indole alkaloids were investigated. Initially, optically active isoquinuclidine derivative 12, a key intermediate for the synthesis of Iboga-type alkaloids, was synthesized via the diastereoselective Diels-Alder reaction of aminodiene 16 with a chiral auxiliary and dienophile 17. Characteristic lactone ring was synthesized via iodolactonization and deiodination. Indole moiety was constructed via Sonogashira cross coupling of alkyne 25and iodoaniline 26 followed by Au catalyzed cyclization. Asymmetric total synthesis of voacangalactone (11) has accomplished by extension of two-carbon unit at C-3 and cyclization of a seven-membered C ring of resulting compound 29. Synthetic 11 was completely identical with natural voacangalactone in all of spectral data. Therefore, the structure of voacangalactone including the absolute configuration was established to be formula 11.Further synthetic study of other Iboga-type indole alkaloids is under investigation in our laboratory.

    View full abstract
  • Yuichiro Hirayama, Kozo Yoneda, Kota Yamagishi, Takumi Chinen, Takeo U ...
    Pages Oral22-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Aplyronine A (ApA) is a marine natural product that shows potent antitumor activity. The primary target of ApA was found to be actin. However, studies on structure-activity relationships and an X-ray analysis of the actin–ApA complex suggested that the potent cytotoxicity of ApA was not accounted for by only interaction with actin, and its molecular targets and mechanisms of action remained unclear.

    To identify the additional target proteins of ApA, we have used the chemical probe approaches. A photoaffinity biotin derivative of ApA (ApA–PB) was synthesized, which remained the activity of ApA sufficiently. With the use of ApA–PB, Arp2 and Arp3 (actin-related proteins) were specifically purified from tumor cell lysate along with actin. However, Arp2 and Arp3 did not covalently bind to ApA–PB. Thus, actin-related proteins might indirectly bind to ApA as the ternary adducts of the actin-ApA complex or through the oligomeric actin.

    In contrast, a new protein has been identified as the secondary target protein of ApA by the photolabeling experiments with ApA–PB in the living tumor cells. In vitro photolabeling experiments using purified proteins and gel filtration HPLC analysis revealed that ApA interacts with the secondary target proteins only in the presence of actin.

    The results of our present study indicate that ApA represents a rare type of natural product which induces protein-protein interaction (PPI) between actin and the secondary target protein to exert highly potent biological activities.

    View full abstract
  • Hidenori Todoroki, Masahumi Iwatsu, Kengo Masuda, Daisuke Urabe, Masay ...
    Pages Oral23-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    4-Hydroxyzinowol (1), a member of dihydo-β-agarofuran sesequiterpenoids, has potent inhibitory activity against P-glycoprotein, which excretes various small molecules across the cell membrane. More than 400 dihydo-β-agarofuran derivatives have been isolated to date, and many of them exhibit various biological activities such as antitumor, anti-inflammatory, immunosuppressive and anti-HIV activities. From the synthetic point of view, the highly oxygenated tricyclic structure of 1 (ABC-ring) decorated with three contiguous tetrasubstituted carbons (C4, 5, and 10) poses a formidable challenge. To establish a general synthetic route to dihydro-β-agarofurans, we selected 4-hydroxyzinowol as the initial synthetic target. Herein we report the stereoselective synthesis of the core structure of 1.

    The synthesis started from 1,5-dihydroxynaphthalene (3). Dearomatization of the B-ring followed by Rhodium-catalyzed asymmetric 1,4-addition of isopropenyl group to enone 11 introduced the three-carbon unit. Hypervalent-iodine promoted C8-hydroxylation of ketone 13 gave 16 stereoselectively. Then, the following 7-step sequence, including stereoselective reduction of C6 and C9 ketones, led to 24, which has four contiguous stereocenters (C6, 7, 8, and 9) of 1.

    The core structure of 1, bearing the three consecutive tetrasubstituted carbons (C4, 5, and 10) was constructed through the following transformations. The dearomatization of 24 with NaIO4 generated the C5-tetrasubstituted carbon via oxidation of the A-ring and simultaneous epoxide formation with the C6 hydroxyl group. The stereo- and regioselective Diels-Alder reaction of diene 26with ethynyl p-tolylsulfone installed the C10-quaternary carbon center to produce 30. Then, the etherification and introduction of the methyl group at C4-ketone realized formation of the C-ring and the three consecutive tetrasubstituted carbons of 1. Finally, the 8-step transformation delivered 41 bearing the entire structure of 1.

    View full abstract
  • Taiki Umezawa, Shohei Yamazaki, Yuko Oguri, Hiroshi Matsuura, Masahiro ...
    Pages Oral24-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Omaezallene (1) was isolated from Laurencia sp. and showed strong antifouling activity against the larvae of the barnacle amphitrite. Although organotin compounds, such as tributyltin (TBT), had been widely used as a fouling inhibitor, the use of TBT was prohibited by IMO in 2008 due to its toxicity. Therefore, the development of the potent nontoxic fouling inhibitor is desired strongly, and 1 is expected to be a lead compound as the fouling inhibitor. Although the relative and absolute structure of 1 was assumed using 1D- and 2D-NMR experiments, the relative configurations have not been determined completely, especially the configuration at C9 position. To determine the relative configurations as well as the absolute configuration, the synthetic study toward 1 was started.

    The synthesis commenced with the known aldehyde 3, derived from D-glucose in 5 steps, which was transformed into the unsaturated ester 8 with E geometry. The ester 8 was next converted to the hemiacetal 10 in 3 steps. The treatment of ethynylmagnesium chloride to 10 afforded the desired propargy alcohol 4 as a major diastereomer. Cyclization of 4 with NBS furnished the construction of the two contiguous stereocenters to give bromoether 11 in a highly stereoselective manner, which was then derived to the aldehyde 6 in 4 steps. 6 was successfully converted to 1via cyanohydrin formation, HWE reaction, and Wittig reaction involving in-situ bromination of reagent. By the total synthesis, the absolute configuration of 1was unambiguously determined as shown in scheme 5.

    View full abstract
  • Shigenobu Umemiya, Yujiro Hayashi
    Pages Oral25-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    A one-pot reaction is an efficient method to achieve several transformations and form several bonds, while at the same time cutting out several purifications, minimizing the generation of waste chemicals, and saving time. Thus, a one-pot reaction can also be regarded as environmentally benign, and “pot economy” should be considered when planning a synthesis.

    The prostaglandins are known to act as local hormones; only trace amounts can control a multitude of important physiological processes, and some of their derivatives are used as medicines. The scientific community has put a great deal of effort and ingenuity into their efficient synthesis because of their biological importance and limited availability from natural sources. These molecules have inspired the chemical community to devise many different synthetic strategies, beginning with Corey’s landmark synthesis and continuing with more than 40 subsequent syntheses, but all the previous syntheses require many operations. Thus, it is still a synthetic challenge to synthesize a molecule of this complexity, that is, with three contiguous stereogenic centers, in a small number of steps and by a sustainable process.

    An efficient total synthesis of prostaglandin E1 methyl ester has been accomplished. The present synthesis has several noteworthy features: 1) The total synthesis was performed in only three pots, including three isolations and three chromatographic purifications, which reduces the amount of solvent necessary and waste formed. 2) The key reaction is a highly selective catalytic reaction, involving an organocatalyst developed by our own group, and reduces the generation of waste. 3) A novel transformation of the nitroalkene into an a, b- unsaturated ketone under mild condition was developed. 4) Protection of the hydroxy group of 17 is not necessary, thus eliminating protection/deprotection steps. 5) The metalbased reagents employed in the present synthesis contain either alkali-metal ions (Na, Li) or nontoxic Zn.

    View full abstract
  • Yu Yamashita, Yoichi Hirano, Akiomi Takada, Hiroshi Takikawa, Keisuke ...
    Pages Oral26-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Antitumor antibiotic BE-43472B was first isolated in 1996 by Banyu from Streptomyces sp. A43472, and recently rediscovered by Rowley from metabolites of marine microorganism synbiotic to a Caribbean ascidian (Ecteinascidia turbinata). In addition to the antitumor activity, the latter study uncovered significant bactericidal activity against drug-resistant pathogens, such as MSSA, MRSA, and VRE. The basic structure is composed of two non-identical anthraquinone moieties connected by a highly hindered carbon–carbon bond. Also notable is the stereochemical complexity associated with the five contiguous stereogenic centers. The important biological activities as well as the uniquely complex molecular architecture have stimulated considerable synthetic interests, and Nicolaou reported the first total synthesis.

    In this talk, we will present the second total synthesis of BE-43472B, featuring: 1) use of isoxazole as a 1,3-diketone surrogate, 2) the isoxazole-directed pinacol 1,2-shift for connecting two anthraquinone precursors at the angular position, and 3) perfect control of five contiguous stereogenic centers. The synthetic route is flexible enough to allow the synthesis of the chiral, non-racemic ones as well as the various congeners with potential biological activities.

    View full abstract
  • Ayumi Tsutsui, Ambara Pradipta, Risa Matsumoto, Koichi Fukase, Katsuno ...
    Pages Oral27-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    We have found that the unsaturated imines derived from the unsaturated aldehydes and ethanolamine derivatives, i.e., phenylglycinol or cis-1-amino-2-indanol, smoothly participated in the [4+4] cycloaddition reaction, providing the 2,6,9-triazabicyclo[3.3.1]nonanes or 1,5-diazaoctanes in almost quantitative yields. The reaction is significantly activated by the presence of the hydroxy groups of the unsaturated imines through (1) novel OH-pinteraction with the reacting imines, and (2) stabilization of the cyclization products. The [4+4] cycloaddition reaction could also proceed from the unsaturated imines containing the amino functionalities; thus, the reaction of acrolein with the polyamines, i.e., spermine or spermidine, readily produced the corresponding 1,5-diazaoctanes at ambient temperature.

    It is known that the polyamines in and on the cells could readily be oxidized by the amine oxidase upon the oxidative stress, resulting in the production of acrolein. Acrolein is the cytotoxic aldehyde, which reacts with the amines or thiols of the biologically relevant molecules, further accelerating the process of oxidative stress. We hypothesized from the reactivity profiles of the unsaturated imines, that the acrolein, which is produced by the polyamines, could react with polyamines themselves, providing the 1,5-diazaoctane derivatives. Spermine as the representative polyamines, smoothly reacted with acrolein, initially producing the 1,5-diazaoctanes, and eventually the hydrogels through the sequential [4+4] polymerization reaction. The [4+4] products of polyamines showed cytotoxicity and promoted the oxidative stress. The results described in this symposium suggest the new mechanism of the oxidative stress underlying the acrolein production from polyamines.

    View full abstract
  • Kei Yamada, Ryo Takahashi, Itaru Sato, Syuji Yamashita, Masahiro Hiram ...
    Pages Oral28-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Cyanosporasides (1, 2) and Fijiolides (3, 4) were isolated from the culture broth of marine actiomyces. These natural products possess a novel cyclopenta[a]- indene framework, which is considered to be a product of cycloaromatization of bicyclo[7.3.0]dodecenediyne (5). Hydrogen and chlorine should be incorporated during the cycloaromatization.

    We succeeded in synthesis of the corresponding bicyclo[7.3.0]dodecenediyne aglycons (17, 32), and demonstrated their cycloaromatization to form the chlorocyclopenta[a]indene structures (21, 22, 35).We found that p-benzyne biradical (19) generated from 9-membered enediyne (17) undergoes a radical monochlorination in Et2O/CCl4 to give selectively 21, and in striking contrast, in the presence of LiCl in DMSO to afford 22 selectively via an ionic pathway. These regioselective monochlorinations were utilized for differential syntheses of protected aglycons of cyanosporasides A and B (23, 24). Protected aglycon of fijiolides (35) was also synthesized via the ionic pathway.

    View full abstract
  • Yuta Kudo, Yamashita Yoko, Konoki Keiichi, Cho Yuko, Yasumoto Takeshi, ...
    Pages Oral29-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Tetrodotoxin (TTX, 1) is a widespread toxin in marine and terrestrial organisms. However, biosynthesis of TTX still remains unknown. We have approached to this issue by identification of natural TTX analogs that might be the biosynthetic precursors of TTX. In the present study, we isolated and determined the structures of two novel analogs of TTX, 4,9-anhydro-10-hemiketal-8-epi-5,6,11-trideoxyTTX (2) and 4,9-anhydro-10-hemiketal-5-deoxyTTX (3) from the newt, Cynops ensicauda popei, together with one novel analog, 6-deoxyTTX (5), from the pufferfish, Takifugu pardalis. Surprisingly, 2 and 3 had the novel skeletal structure in which an ether (C5-O-C10) in TTX is replaced by a C5-C10 bond. Base on the structure of 3, we hypothesized new biosynthetic pathways of TTX assuming geranyl phyrophosphate (GPP) as the starting material. GPP would be first aminated, and then transformed to the guanidine derivative by amidinotransferase. Subsequently, cyclization of the guanidine would trigger sequential cyclization of geranyl unit to form the skeletal structure of 3. After several oxidation steps including Baeyer-Villiger oxidation, TTX would be formed via 4,9-anhydroTTX.

    View full abstract
  • Genta Tadano, Keiji Tanino
    Pages Oral3-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Altemicidin (1), which was isolated from the Actinomycetestrain Streptomyces sioyaensis SA-1758 by Takeuchi et al. in 1989, exhibits anti-brine shrimp activity as well as acaricide and antitumor activity. The total synthesis of altemicidin was accomplished on the basis of original strategy involving, (1) an intramolecular Mizoroki-Heck reaction of bromopyridine 19 for the construction of the five-membered ring, and (2) the stereoselective partial reduction of methyl pyridinium salt 23 leading to the hexahydro-6-azaindene skeleton.

    Bromopyridine 19 was synthesized from cyano pyridine 17 through an addition reaction with a,b-unsaturated aldehyde 6 followed by protection of the resulting alcohol with a TIPS group. The intramolecular Mizoroki-Heck reaction of 19 was performed by adopting the optimized conditions using Pd(OAc)2 and P(2-furyl)3as the catalyst in CH3CN at 130 °C under irradiation of microwave, resulting in formation of cyclization product 20. While product 20 was found to be the wrong diastereomer, treatment of the corresponding ester 21 with TBAF effected inversion of the configuration of the hydroxyl group. Then the stereoselective partial reduction of the pyridine ring was achieved through reduction of methyl pyridinium salt 23 with NaBH4, protection of the hydroxyl group with a TES group, and hydrogenation of tetrahydropyridine 27 catalyzed by Pd/C. Finally, the total synthesis of altemicidin was accomplished by elaboration of the functional groups (17 steps in total, 1.8% overall yield).

    View full abstract
  • Tsutomu Hoshino, Akifumi Chiba, Naomi Abe, Masaki Hanaoka, Yuuki Yamag ...
    Pages Oral30-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Triterpene cyclases convert a linear molecules of squalene (SQ) and/or oxidosqualene (OXSQ) into a variety of cyclic triterpene scaffolds. The enzymatic reactions proceed with complete regio- and stereospecificity. The structural diversity of triterpene is remarkable. In this symposium, we discuss mainly the biosyntheses of lanosterol and b-amyrin synthases from the point of view of how the methyl groups on squalene backbone exert influences on the polycyclization cascade. Now we must accept the new concept that lanosterol synthase folds oxidosqualene in a chair/boat/chair/chairconformation in the enzyme cavity, although some researchers frequently describe the incorrect folding conformation, i.e., chair/boat/chair/boat.The pioneering works using norOXSQ analogs by van Tamelen and Corey groups have revealed that Me-26 and Me-28 make little effect on the folding conformation to yield lanosterol skeleton. Corey et al reported that 27,28-bisnorOXSQ was folded in an unusual chair/chair/boat conformation by lanosterol cyclase, generating an intriguing product called a pendant-like compound 11 (6/6/5+4). Comparing the incubation result of 28-norOXSQ with that of 27, 28-bisnorOXSQ, Corey et al. concluded that Me-27 is critical to the formation of the correct folding. However, neither experiment of 27-norOXSQ nor that of 29-norOXSQ has been reported. Incubation of 27-norOXSQ with lanosterol cyclase afforded products 12 and 13 (9:1), which were generated via normal conformation (chair/boat/chair/chair) and incorrect conformation (chair/chair/boat), respectively. Enzymatic reaction of 29-norOXSQ gave two novel compounds 14and 15 (4:5) that consist of a 6/6/6/6-fused tetracycle. Product 14could be produced through a normal folding, but 15 was generated via an abnormal chair/chair/boat/chair conformation. Thus, it can be concluded Me-29 is most crucial to the formation of lanosterol rather than Me-27.

    On the other hand, studies on b-amyrin synthase employing the substrate analogs are limited. Recently, we succeeded in the functional expression and expedient preparation of pure b-amyrin synthase. We synthesized 24-nor and 30-norOXSQ in order to inspect the role of the Me groups for b-amyrin biosynthesis. 30-NorOXSQ gave 9 products that consist of 6/6/6/5- and 6/6/6/6-fused tetracycles and 6/6/6/6/6-fused pentacycle, which were produced via normal and unusual folding conformations. On the other hand, 24-norOXSQ gave two products as main products, all of which was generated exclusively via a normal folding conformation. Thus, b-amyrin cyclase more tightly binds to Me-30 (Z-Me) than Me-24 (E-Me), leading to the correct folding of a chair/chair/chair/boat/boat conformation. In other words, Me-30 is essential to the formation of pentacyclic oleanyl cation.

    Previously, we reported that Me-27 is most crucial for hopene biosynthesis. Furthermore, a lacking of either Me-24 or Me-30 afforded a tetrahymanol skeleton, indicating the occurrence of the loose binding. The affinity difference toward the branched Me groups differently positioned on the substrate molecule would impose the different conformation, which would then lead to the structural diversity of naturally occurring triterpenes.

    View full abstract
  • Keita Amagai, Ryoma Takaku, Fumitaka Kudo, Tadashi Eguchi
    Pages Oral31-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Cremimycin is a 19-membered macrolactam glycoside antibiotic isolated from Streptomyces sp. MJ635-86F5, showing broad spectrum against Gram-positive bacteria. A characteristic acyl-side chain-containing β-amino acid, 3-aminononanoate was presumed to be the starter unit of the polyketide chain elongation, even though the biosynthetic pathway for 3-aminononanoate has not been recognized. Because we are interested in the biosynthetic engineering of β-amino acid-containing macrolactam machineries by swapping of the starter units, we have been collecting some related biosynthetic gene clusters including vicenistatin and incednine biosynthetic genes. In the present study, we have identified the cremimycin biosynthetic gene clusters and characterized 3-aminononanoate forming enzymes.

    A gene cluster harboring the genes encoding polyketide synthetases (PKS), deoxysugar biosynthetic enzymes, and characteristic enzymes for β-amino acid-containing macrolactam biosynthesis, was identified by a conventional hybridization method. Involvement of the gene cluster in the cremimycin production was confirmed by a gene inactivation experiment. By comparison with the biosynthetic genes for cremimycin, BE-14106 and ML-449, a characteristic operon that encodes a fatty acyl-CoA thioesterase (FcoT), a truncated PKS, and a FAD-dependent glycine oxidase was found to be conserved. Thus, we hypothesized the involvement these proteins in the common biosynthetic pathway for the acyl side chain-containing β-amino acid moieties. CmiS1 (FcoT) and CmiS2 (glycine oxidase) were expressed heterologously in E. coliand their functions were analyzed in vitro with candidate substrate analogs. Consequently, it appeared that CmiS1 catalyzes Michael addition of glycine to 2-nonenoyl thioester and hydrolysis of the thioester, then CmiS2 oxidizes the carboxymethyl moiety of CmiS1 product to afford 3-aminononanoate. Incorporation of deuterium labeled 3-aminononanoate into cremymycin during the culture of producer strain supported its involvement in the biosynthetic pathway as an intermediate. The characterized amino-transfer mechanism catalyzed by CmiS1 and CmiS2 is quite different from PLP-dependent transamination and aminomutase type reactions and thus a new entry to the β-amino acid biosynthetic machineries.

    View full abstract
  • Atsushi Minami, Koichi Tagami, Ryota Chiba, Ryuya Fujii, Chengwei Liu, ...
    Pages Oral32-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Fungi are one of the most important biological sources of natural products. They produce various types of secondary metabolites such as polyketide, non-ribosomal pepteide, isoprenoid, and alkaloid. In addition, recent fungal genome analysis shows the presence of numerous gene clusters for biosynthesis of secondary metabolite, most of which are not expressed. Thus, establishment of reliable gene expression system is important for the reconstitution of the biosynthetic machinery and total biosynthesis of fungal metabolites.

    Aspergillus oryzae expression system is found to be a powerful method for functional analysis of biosynthetic genes involved in fungal secondary metabolites, because transformantion of plasmids with target gene enabled us to isolate expected biosynthetic intermediate/product from the transformant. This heterologous expression system was extended to the total biosynthesis of natural products such as tenellin, penicillin, and aphidicolin. Accumulated examples of heterologous production of fungal metabolites prompted us to analyze the biosynthetic machinery of complex natural products and the function of functionally unidentified genes found in fungal genome project. Here we present most recent results including (i) reconstitution of biosynthetic machinery and total biosynthesis of indole diterpene paxiline and (ii) identification of ophiobolin F synthase by a genome mining approach. These results suggest that heterologous expression in A. oryzae can be applied to produce known or unknown natural products for which biosynthetic genes are available.

    View full abstract
  • Yudai Matsuda, Takayoshi Awakawa, Toshiyuki Wakimoto, Ikuro Abe
    Pages Oral33-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    The fungal meroterpenoids derived from 3,5-dimethylorsellinic acid (DMOA) comprise a quite large number of structurally diverse molecules, including terretonin, austinol, and andrastin A.These compounds share the common pre-cyclization precursors in their biosyntheses but differ due to variations in the cyclization and tailoring reactions on the complex multicyclic scaffolds. We revealed the functions of the enzymes responsible for these reactions by expressing them in the heterologous host, Aspergillus oryzae.

    First, we characterized the functions of three terpene cyclases Trt1, AusL, and AdrI, which are involved in the biosyntheses of terretonin, austinol, and andrastin A, respectively. They all accept the same substrate epoxyfarnesyl-DMOA methyl ester but produce differently cyclized products. Interestingly, they do not utilize the desmethyl substrate analogue with a free carboxyl group, indicating that the methyl esterification is an essential factor for their biosyntheses.

    Then, we turned our attention to the post-cyclization tailoring reactions. As for austinol biosynthesis, despite the previous gene disruption and reconstitution studies, the biosynthetic pathway of preaustinoid A3 from protoaustinoid A remained a missing link. In this study, we characterized the reaction of three oxygenases, a spiro-ring forming dioxygenase, AusE, and two flavin-dependent monooxygenases, AusB and AusC, which are responsible for the bioconversion of protoaustinoid A into preaustinoid A3.

    We also report the complete biosynthetic pathway of andrastin A, which includes four tailoring reactions catalyzed by AdrF, AdrE, AdrJ, and AdrA.

    View full abstract
  • Chengwei Liu, Atsushi Minami, Motoyoshi Noike, Koichi Tagami, Hideaki ...
    Pages Oral34-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Paxilline (3) is an indole diterpene produced by Penicillium paxilli. Six genes (paxB, C, G, M, P, and Q) in the 3 biosynthetic gene cluster were previously shown to be responsible for 3 biosynthesis. In this study, we have characterized paxC and paxD, which are located in the paxilline biosynthetic gene cluster and have homologies to fungal prenyltransferase genes. Both enzymes were overexpressed inE. coli and the purified enzymes were used for in vitro analysis. Recombinant PaxC used indole-3-glcerolphosphate and indole as prenyl accepters and geranylgeranyl diphosphate and farnesyl diphosphate as prenyl donors. When 3 and dimethylallyl diphosphate were used as substrates, PaxD catalyzed the formation of one major and one minor product, which were identified as di-prenyl paxilline and mono-prenyl paxilline by LC-MS analysis. The structure of the major product was determined to be 21,22-diprenylated paxilline (4), showing that PaxD catalyzed the successive di-prenylation. We also investigated a function of atmD, which is located in the aflatrem (10) biosynthetic gene cluster in Aspergillus flavus and encodes an enzyme with 32% amino acid identity to PaxD, When 3 and DMAPP were used as substrates, the two major and a trace of minor product were formed. Structures of the two major products were determined to be reversely mono-prenylated paxilline, (5) and (6), at either the 20- or 21-position. Since 10 and β-aflatrem (11), both of which are 3-related compounds produced by A. flavus,have the same prenyl moiety at the 20- and 21-position, respectively, AtmD should catalyze the prenylation in 10 and 11 biosynthesis. More importantly and surprisingly, AtmD accepted paspaline (2), which is an intermediate of 3 biosynthesis that has a similar structure to 3, but the position and regular/reverse specificities for prenylation were unexpectedly altered. AtmD catalyzed a regular mono-prenylation of 2 at either the 21- or 22-position though the reverse prenylation was observed with 3, suggesting that fungal indole diterpene prenyltransferases have the potential to alter their position and regular/reverse specificities for prenylation.

    View full abstract
  • Yuta Tsunematsu, Takayoshi Saruwatari, Tomohiro Sugiyama, Hiroki Kato, ...
    Pages Oral35-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    In recent years, many secondary metabolite gene clusters, including polyketide biosynthetic genes, non-ribosomal peptide synthetase genes have been uncovered through fungal genome sequencing. However, several transcriptome analyses revealed that a lot of biosynthetic genes are not activated in conventional culture condition. If we can systematically activate such silent biosynthetic gene clusters with genetic modification, it has a possibility of discovering novel natural products with previously unidentified unique structure and biological activities. In this study, we focused putative transcription factor (TF) genes which locating in the biosynthetic gene cluster. We conducted strong activity promoter-based overexpression of TFs in Aspergillus niger, Chaetomium globosum, Arthroderma otae, Trichophyton equinum, and could successfully biosynthesize secondary metabolites 1-9. These chemical structures were characterized based on MS and NMR spectroscopic analysis. The comprehensive relationship between gene clusters and natural products has allowed us to provide insight into their biosynthetic pathway.

    View full abstract
  • Ning Wang, Mizuho Hasegawa, Akiyoshi Hirata, Naohiro Inohara, Kiyoshi ...
    Pages Oral36-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Bacterial cell wall peptidoglycan (PGN) has been known as a potent immunopotentiator. Recently, various proteins that recognize PGN have been reported, such as nucleotide-binding oligomerization domain protein 1 (Nod1) and 2 (Nod2), peptidoglycan recognition proteins (PGRP), and lectins. However, the comprehensive analyses of their substrate structures have not been really conducted because of the lack of pure chemically synthesized PGN fragments. In this work, PGN fragments library including two kinds of sequences of alternating glycans (GlcNAc/MurNAc) with various length of glycan chains were synthesized. The targets covered the compounds having disaccharide, tetrasaccharide, and octasaccharide. The Nod2 stimulating activity of each synthetic peptidoglycan fragment was then evaluated. A notable difference between MGMG and GMGM sequence of PGN fragments was observed for the first time. MGMG sequence fragments showed higher activity than the corresponding GMGM fragments having the same peptides.

    Construction of PGN arrays was performed by attaching synthesized PGN fragments on a solid surface of the array platforms. In order to introduce the PGN fragments to the array, several linkage structures were examined, and finally a linker with terminal amine was successfully attached to the PGN fragments. Human PGRP-S with combination of fluorescence labeled antibody was used for evaluation of the array. PGRP-S bound to GMGM3 and GMGM4 more tightly than GMGM2. The result was also reproducible in SPR analysis. PGN partial structure library and their microarray were successfully constructed. This work enabled the study of the precise PGN structures responsible for the interactions with various PGN-binding proteins.

    View full abstract
  • Satomi Shimura, Masahiro Ishima, Ikue Ota, Etsuko Tsutsui, Shinji Kami ...
    Pages Oral37-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    MA026, a novel lipocyclodepsopeptide, was isolated from the fermentation broth of Pseudomonas sp. RtIB026 found in digestive tracts of rainbow trout. This natural product exhibits antiviral activity against infectious hematopoietic necrosis virus (IHNV) and several enveloped viruses. MA026 has a potential to create a novel antiviral drug and more biological characterizations are required. To conduct further studies to reveal the mode of action, a flexible chemical synthesis and modifications are essential. Herein, we provide the first total synthesis of MA026 and phage display screening to identify the target. MA026 consists of cyclodepsipeptide, chain peptide and N-terminal (R)-3-hydroxydecanoic acid. To maximize the convergency, MA026 was divided into two key segments, side chain 2 and cyclodepsipeptide 3. Key to the preparation of 3 was the macrocyclization of decadepsipeptide which relies on the macrocyclization site. Two macrocyclization sites were examined and the macrocyclization at D-Gln11-L-Leu12 furnished cyclodepsipeptide 3 successfully. To reveal the mechanism of antiviral activity, we synthesized biotinylated MA026 and MA026-immobilized PEGA resins. Phage display screenings using these probes were performed to afford peptide sequences that would interact with MA026.

    View full abstract
  • Masayuki Izumi, Simone Dedola, Tatsuto Kiuchi, Rie Kuruma, Yutaka Maki ...
    Pages Oral38-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    UDP-glucose:glycoprotein glucosyltransferase (UGGT) is one of the key player in a glycoprotein quality control (QC) system. It is known as a folding sensor enzyme since it distinguishes misfolded glycoproteins from correctly folded one and transfers glucose preferentially to misfolded glycoprotein bearing high-mannose type N-glycan which serves as a tag for refolding. To study glycoprotein QC system at molecular level, misfolded homogeneous glycoproteins bearing high-mannose type oligosaccharide were synthesized as substrates of UGGT.

    First, we designed a model glycoprotein based on interleukin 8 (IL-8) and incorporated high-mannose type (Man9GlcNAc2) oligosaccharide to Asn36. Chemically synthesized full-length glycosylated polypeptide was used for extensive folding experiments which gave correctly folded glycoprotein as well as misfolded glycoproteins with non-native disulfide bond patterns. Glucose transfer to all misfolded glycoproteins were observed by LC-MS, however native glycoprotein was merely glucosylated. Then, we prepared a library consists of 10 glycopeptides which differ in only one amino acid residue at the same position and examined as substrates of UGGT. Glucosylation rate was different for each glycopeptide suggesting that even one amino acid can influence the substrate recognition of UGGT. We also prepared a glycopeptide labeled with 15N at selected residues for the interaction study with UGGT using NMR. Clear chemical shift change was observed for only one peak by titration study suggesting the specific interaction between UGGT and the peptide part of the glycopeptide. We also examined the ability of UGGT to glucosylate folding intermediates by performing folding experiment in the presence of UGGT. All glycoproteins including native structure were glucosylated suggesting that folding intermediates were substrates of UGGT. We also found that erythropoietin bearing only one oligosaccharide instead of native three oligosaccharides was also glucosylated by UGGT. This may indicates the ability of UGGT to recognize glycosylation defects of glycoproteins through exposed hydrophobic surface normally covered by oligosaccharide.

    View full abstract
  • Takashi Muto, Kumiko Sekine, Haruhiko Fuwa, Makoto Sasaki
    Pages Oral39-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Didemnaketals A, B, and C were isolated from the extract of the magenta ascidian Didemnum sp. collected at Auluptagel Island in Palau by Faulkner and co-workers. The gross structures of didemnaketals were determined by extensive 2D-NMR spectroscopic analyses. The absolute configuration of didemnaketal B was subsequently proposed on the basis of degradation/derivatization experiments, X-ray crystallographic analysis, and application of chiral anisotropic reagents. However, the total synthesis of a structural homologue didemnaketal A by Tu and co-workers questioned the stereochemical assignment made by Faulkner et al. Here we describe the first total synthesis of the proposed structure 2 of didemnaketal B, which featured (1) our spiroacetal synthesis strategy exploiting Suzuki−Miyaura coupling for the C7−C20 domain; (2) Evans syn-aldol and vinylogous Mukaiyama aldol reactions for the C1−C7 acyclic domain; and (3) a Nozaki−Hiyama−Kishi reaction for a late-stage introduction of the C21−C28 side chain. However, the NMR spectroscopic properties of synthetic 2 did not match those of authentic didemnaketal B. Careful comparison of the NMR spectroscopic data of synthetic 2 with those of the authentic sample as well as the application of the phenylglycine methyl ester (PGME) method to a C7−C20 spiroacetal model compound led us to postulate that the absolute configuration of the C10−C20 domain of 2 has been erroneously assigned. Accordingly, we revised the structure of didemnaketal B to be shown by 30, which was eventually verified by our total synthesis. Thus, we have established the complete stereostructure of didemnaketal B.

    View full abstract
  • Takaaki Sato, Kenji Shirokane, Takamasa Wada, Makoto Yoritate, Ryo Min ...
    Pages Oral4-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

      Modern organic chemistry has resulted in the need for compounds ever increasing complexity. However, reactions of a targeted functional group in such a complex molecules often require extra steps to protect more reactive functional group. As one of the solution to overcome this challenges, we developed a chemoselective reductive nucleophilic addition to N-methoxyamide 5 (Table 2). Exposure of 5 to the Schwartz reagent gave 7, which was treated with catalytic amount of Sc(OTf)3 and allyltributylstannane to give substituted amine 9. The developed conditions exhibited extremely high chemoselectivity, and are compatible with a number of functional groups including esters, nitros, nitriles, alkyl halides, carbamates, sulfonamide, olefins and acetals.

    To demonstrate the practical utility of the chemoselective reductive allylation, we applied this methodology to the total synthesis of gephyrotoxin (31). The first key reaction was a direct coupling of N-methoxyamide 26 with aldehyde and the subsequent intramolecular allylation, giving the cis cyclic compound 28 as a single diastereomer (Scheme 3). The next challenge was the chemoselective reductive allylation of bicyclic lactam 29 (Scheme 4). The reaction proceeded in complete chemoselective fashion in the presence of more electrophilic ester than the N-methoxylactam. Our cheomoselective approach minimized use of protecting group manipulations, and resulted in the concise total synthesis of gephyrotoxin (31).

    View full abstract
  • Kazutada Ikeuchi, Moemi Hayashi, Tomohiro Yamamoto, Makoto Inai, Tomoh ...
    Pages Oral40-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Sphingofungin E (1) is an a-disubstituted-a-amino acid isolated from Paecilomyces variotii in 1992 by Merck group, which shows potent immunosuppressant activity. Previously, we reported total synthesis of myriocin (2) which lacks a hydroxy group at C-5 position. Moreover, we recently succeeded in asymmetric bromolactonization of symmetric cyclic carboxylic acid 3 by employing the combination of NBS and (DHQD)2PHAL. Based on these results, we herein described the total synthesis of 1.

    Asymmetric desymmetrization of 12 with (DHQD)2PHAL (3 mol%) afforded 13 in 99% with 90% ee. The introduction of a hydroxy group at the C-5 position was achieved via Mn (III)-catalyzed allylic C-H oxidation followed by 1,2-reduction to obtain allylic alcohol 15 in good yield with high diastereoselectivity. The four contiguous stereogenic centers of 1 were constructed by Mitsunobu reaction using p-nitrophenol, followed by regioselective epoxide-opening reaction to give 19 stereoselectively. In the first approach of regioselective olefination, Wittig olefination with a stable ylide was exaimed. But, the several results revealed that ozonolysis of ester 37 followed by Takai olefination with diiodoalkane 35 was more effective elongation to obtain (E)-olefin 38 in good yield. The remaining aldehyde was converted to amide 41 via cyanohydrin formation, followed by AZADO oxidation. The obtained amide 41 was subjected to Hofmann rearrangement with PhI(OCOCF3)2 to give the mixture of oxazolidinone 44 and 45,which have a-disubstituted-a-amino acid skeleton. Finaly, all protecting groups were removed to complete the synthesis of (-)-sphingofungin E (1).

    View full abstract
  • Hayato Ishikawa, Shinji Tadano, Yuri Mukaeda
    Pages Oral41-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    A large number of tryptophan-based dimeric diketopyperadine (DKP) alkaloids which show fascinating biological activities, were isolated from fungi. Direct bio-inspired dimerization reactions along with an originally proposed biosynthetic pathway from commercially available amine-free tryptophan derivatives in aqueous acidic media using Mn(OAc)3, VOF3, or V2O5as one-electron oxidants were developed to provide C2-symmetric and non-symmetric dimeric compounds. In addition, concise two-pot or three-step syntheses of naturally occurring dimeric diketopiperazine alkaloids (+)-WIN 64821, (–)-ditryptophenaline, (+)-naseseazine B, (+)-WIN 64745, and (+)-asperdimin were accomplished in total yield of 20%, 13%, 20%, 17%, and 15% respectively. The present synthesis has several noteworthy features: 1) Tryptophan based C2-symmetric and non-symmetric dimeric key intermediate can be prepared multigram scale in one step at same time. 2) Developed oxidation reaction was carried out in acidic water solution without deactivation of metal oxidants. 3) The protection on primary amine can be avoided by salt formation in acidic water in the synthetic scheme. 4) In total two-pot operation, the reaction media are only environmentally friendly water and ethanol. 5) Satisfied total yields are obtained compared with previous reported synthesis. 6) No special care is needed to exclude water or air. 7) Effective Boc deprotection and diketopiperazine formation in one step was discovered under vacuum condition.

    View full abstract
  • Hirotatsu Umihara, Yumi Yoshino, Jun Shimokawa, Masato Kitamura, Tohru ...
    Pages Oral42-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Erythrina alkaloids, isolated from Erythrina genus, have attracted the attention of synthetic chemists for decades because of their wide range of biological activities and unique structures. While extensive synthetic studies of the erythrina alkaloids have been conducted to date, asymmetric synthesis takes up a small portion because of its inherent difficulty.

    Our retrosynthetic analysis of erythraline (1),2 one of the representative members of the erythrina alkaloids, was performed on the basis of its biosynthetic pathway.1 As outlined in Scheme 4 and 5, Suzuki-Miyaura coupling of readily available, optically active aryl bromide 20 and aryl boronate 9gave the biaryl intermediate. Lactamization of 21, after deprotection, gave 9-membered lactams, 22and 23, indicating the presence of the axial chirality. After thermal isomerization 6 and protection, the key intermediate 25was obtained as a single isomer. Oxidation of the phenol by means of singlet oxygen and subsequent transannular Michael addition was achieved after extensive investigation to give the polycyclic compound 26 as a single isomer. The oxidation state of 27was adjusted in several steps 3 to accomplish the first asymmetric total synthesis of erythraline (1).

    We are currently investigating a more efficient strategy for the preparation of optically active 23 (Scheme 6). During the course of this investigation we found the facile epimerization of the axial chirality of ketone 28 at room temperature. Thus, CBS reduction of 28 was conducted to afford 23 in a reasonable enantiomeric ratio. Further investigation along this line is currently underway.

    In conclusion, we have established an efficient method for the construction of the core skeleton of erythrina alkaloids. The intermediate 26 has the potential for the application to the syntheses of a variety of erythrina alkaloids.

    View full abstract
  • Masato Takahashi, Noriyuki Suzuki, Tsutomu Ishikawa, Ih-Sheng Chen
    Pages Oral43-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    We have explored a novel method to synthesize chiral 3-aryl(or -unsaturated) aziridine-2-carboxylates, which could be potential precursors of natural products such as alkaloids and lignans. Here, we will present synthetic studies on (-)-podophyllotoxin (1) and new dimric phenylpropanoids 2 from 3-arylaziridine-2-carboxylates.

    For approach to (-)-podophyllotoxin (1), the starting 3b was prepared in 84% yield and with 82% ee by asymmetric aziridination. Treatment of 3a with sesamol (8j) in the presence of Zn(OTf)2 afforded a desired carbon-inserted ring-opened product 4j. Vinyl-inserted product 5 was smoothly given from 4j by CN bond cleavage, trifluoromethanesulfonation, and Pd-coupling reaction. The ee of 5 was estimated as 81%, which wasincreased to 99% after recrystallization. Chemical manipulations of 5 successfully provided Meyers’ intermediate (17) and Zhang’s intermediate (19), which had been converted to (–)-podophyllotoxin (1).

    View full abstract
  • Satoru Yamaguchi, Daisuke Yuyama, Nobuyuki Takahashi, Keisuke Suzuki, ...
    Pages Oral44-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Dermocanarin 2 (2) is a naturally occurring pigment, in which an anthraquinone and a naphthoquinone are directly connected through a sigma bond and bridged by nine–membered lactone structure. Hindered rotation of the Csp2–Csp2bond between the quinone moieties renders axial chirality, and a stereogenic center exists in the lactone portion. Construction of the unique hexacyclic framework and rigorous control of absolute and relative stereochemistry make this compound a challenging synthetic target.

    In this presentation, we report the first total synthesis of dermocanarin 2 (2). Key steps of the synthesis include (1) desymmetrization of s-symmetric biphenyl diacetate 11 by means of enzyme to afford axially chiral biphenyl 10 in an enantiomerically pure form (Scheme 2); (2) highly diastereoselective addition of ester enolate to the ketone moiety of biphenyl 9 to construct the C3’ stereogenic center (Table 1); (3) facile construction of the anthraquinone framework via the consecutive electrocyclization reactions of benzocyclobutene moiety under heating (Scheme 3, 22→23); (4) regioselective Diels–Alder reaction of the chlorobenzoquinone moiety in 25 with siloxy diene 6 to construct the naphthoquinone framework (Scheme 4, 25→26); (5) formation of the nine-membered lactone from the non-protected precursor 4, leading to the finish of the total synthesis (Scheme 4, 4→2).

    View full abstract
  • Takeo Sakai, Shingo Matsushita, Haruka Asano, Rie Oshima, Kouichi Mori ...
    Pages Oral45-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Gymnocin-A (1) is a marine-derived polycyclic ether natural product having cytotoxicity in P388 mouse leukemia cells (IC50: 1.3 mg/mL). This marine toxin with a very large chemical structure was isolated from Karenia mikimotoi, a dinoflagellate of the red tide, which caused severe losses to the fishery industry. Because only a small amount of 1 could be isolated from the natural sources, the total synthesis of 1 becomes important to supply enough material for further biological studies.

    The retrosynthetic analysis is based on our [X + 2 + Y]-type convergent strategy. When the point of convergence is between the DE and IJ-rings, 1 is divided into three fragments: an ABC-fragment (2), an FGH-fragment (3), and a KLMN-fragment (4). The synthesis of each of these fragments 2–4 was also planned using the oxiranyl anion convergent strategy from units 5–8 (Schemes 1 and 2).

    1) Synthesis of units 6–8

    Units 6, 7, and 8 were synthesized using 2-deoxy-d-ribose as the common starting material in 7, 14, and 12 steps, respectively (Scheme 3). The synthesis of F/K unit 7 is shown in Scheme 4. The SmI2-induced radical cyclization of aldehyde 10, which was synthesized from 2-deoxy- d-ribose in five steps, afforded 11 in good yield. Triflate 7 was synthesized in eight steps.

    2) Synthesis of ABC-fragment

    First, we studied the convergent strategy for triflate 5 and epoxysulfone 6. However, the cyclization of 16 failed owing to the strain in trans-substituted five-membered A-ring of 16 (Scheme 5). Therefore, we adopted another route in which the five-membered A-ring was introduced after the construction of BC rings. The oxiranyl anion convergent strategy was applied to triflate 18 and 19 to afford six-membered ketone 22. After the ring-expansion reaction, the a-hydroxyl group was selectively introduced by the oxidation of TES-enol ether to afford 23. The removal of TBS group using TsOH followed by reductive etherification afforded 24, and thus, the synthesis of the BC-ring system was completed. The A-ring was formed by the radical cyclization of iodide 26using Et3B and n-BuSn3H (Scheme 6).

    3) Synthesis of FGH-fragment model

    The GH and LM rings, a point of convergence between the FGH and KLMN fragments, possess the same ring system. A key step in the synthesis of both fragments involves the intramolecular substitution reaction of a tertiary alcohol to a bromoketone. 30 underwent cyclization in the presence of sodium hydride to afford the cyclized product 31 in good yield; however, this reaction showed poor reproducibility when the sodium hydride from a newly opened bottle was used. The ring expansion followed by reductive etherification afforded FGH-fragment model 34 (Scheme 7).

    4) Synthesis of KLMN-fragment

    Using the oxiranyl anion strategy, triflate 7 and epoxysulfone 8 were reacted to afford the coupling product 35. Although initially cyclized product 37 was obtained in poor yield using sodium hydride, it was finally found that a 10% aqueous NaOH solution efficiently promoted this cyclization reaction of bromoketone 36. The ring expansion followed by reductive etherification completed the synthesis of KLMN ring system (39). Finally, the synthesis of KLMN-fragment 6 was achieved in six steps from 39.

    [1](a) Tsukano, C.; Sasaki, M. J. Am. Chem. Soc. 2003, 125, 14294–14295. (b) Tsukano, C.; Ebine, M.; Sasaki, M. J. Am. Chem. Soc. 2005, 127, 4326–4335.

    [2](a) Sakai, T.; Sugimoto, A.; Mori, Y. Org. Lett. 2011, 13, 5850–5853. (b) Sakai, T.; Sugimoto, A.; Tatematsu, H.; Mori, Y. J. Org. Chem. 2012, 77, 11177–11191.

    View full abstract
  • Masaatsu Adachi, Takuya Imazu, Ryo Sakakibara, Yoshiki Satake, Minoru ...
    Pages Oral46-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Tetrodotoxin (TTX, 1), a well-known marine natural product, was originally isolated as a toxic principle of puffer fish intoxication. The toxicity is attributed to a specific blockage for voltage-dependent sodium channels responsible for nerve and muscle excitability. Chiriquitoxin (CHTX, 2), a naturally occurring analog of TTX, was first isolated from the skin of harlequin Costa Rica frog, Atelopus chiriquiensis. The structure of CHTX including all absolute configurations was elucidated on the basis of extensive spectroscopic analyses by Yotsu-Yamashita and Yasumoto in 1990. CHTX possesses the same basic structure of TTX, except that it has a glycine residue attached to the C-11 position. Although CHTX was reported to interfere with both sodium and potassium channels, the details are still unsolved because of the limited availability of 2 from natural sources. Thus, we initiated synthetic studies toward the total synthesis of CHTX (2).

    The synthesis commenced with allylic oxidation at C-5 position of hydroxylated compound 3. The resulting 9 was transformed into aldehyde 11 through epoxidation and ozonolysis of the vinyl group. Addition of lithium acetylide as a carboxylic acid equivalent to aldehyde 11gave a 10:1 diastereomeric mixture in favor of the desired product 12. Then, 12 was transformed into diacetate 15, and acetylenic moiety of 15 was cleaved with RuCl3 and OxoneRfollowed by alkaline hydrogen peroxide to give the carboxylic acid intermediate, which underwent spontaneous opening of the epoxide, as expected. Subsequent silylation provided orthoester 16 in good overall yield. Selective deprotection of the acetonide and subsequent cleavage of the resulting 1,2-diol gave an aldehyde, which was protected as internal acetal.

    Toward the total synthesis of CHTX (2), introduction of a glycine residue at the C-11 position by aldol reaction was examined. After one-pot transformation from trichloroacetamide of 17 into benzyl carbamate, MTM-protected aldehyde 21 was synthesized in 2 steps. Addition of lithium enolate generated from iminolactone 22 to aldehyde 21 proceeded in a highly stereoselective manner, yielding the desired anti-aldol adduct 23 as a single product. Hydrogenolytic deprotection of Cbz group of 23 and subsequent guanidinylation gave di-Boc guanidine 24. Since deprotection of the MTM group under the conventional conditions failed to give the expected alcohol, we developed a new deprotection method of MTM group by utilizing Pummerer reaction; oxidation of 24 with MCPBA was followed by treatment of the resulting sulfoxide 25 with TFAA to give mono-thioacetal 26. Then, sequential hydrolysis provided diol 27. Deprotection of all the protecting groups of 27 with aqueous HF provided 4,9-anhydroCHTX-13,6-lactone (28), which was further treated with aqueous pyridine to furnish CHTX (2). The NMR spectra of the synthesized 2 were identical to those of the natural chiriquitoxin.

    View full abstract
  • Hideto Fujiwara, Taichi Kurogi, Shun Okaya, Kaori Yamada, Malipan Sapp ...
    Pages Oral5-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Acetylaranotin (1), which was isolated from a fungus Arachniotus aureus in 1968, displays intriguing biological activities such as inhibitory activity against viral RNA polymerase. In addition to these important biological activities, the unique dimeric structure, possessing highly functionalized dihydrooxepine rings fused to pyrrolidino-diketopiperazine skeleton, has attracted considerable attention as one of most challenging target from the synthetic community. Herein, we describe total synthesis of (–)-acetylaranotin featuring vinylogous Rubottom oxidation and formation of the characteristic dihydrooxepine ring and structural determination of its congener.

    Synthesis of the dihydrooxepine bearing a hydroxyl group at the g-position commenced with introduction of a hydroxyl group at the g-position of cyclohexenone, which is a common structure in the related compounds. We developed a regio- and stereoselective introduction of the hydroxyl group at the g-position of the cyclohexenone derivative by a regioselective dienol silyl ether formation and subsequent unusual vinylogous Rubottom oxidation. After protection of the alcohol 17 as its TBS ether, regio-controlled Baeyer-Villiger oxidation of the silyl ether 18 provided seven-membered enol lactone 19, which was converted to dihydrooxepine 21 via reduction of the corresponding triflate 20. Next, we focused on the crucial condensation of two monomer units. Remarkably, the use of a monomer unit with unnatural stereochemistry was crucial for the smooth condensation and formation of the diketopiperazine 25. The remaining task was inversion of two hydroxyl groups, which was executed by an exceptionally efficient oxidation using Iwabuchi’s nor-AZADO and Luche reduction at low temperature. The facial selectivity in the reduction was completely controlled by the steric bias of the densely fused polycyclic skeleton, which led to the total synthesis of acetylaranotin (1). We also determined the stereochemistry of the related compound, hirsutellomycin (5).

    View full abstract
  • Yu Kobayakawa, Masahisa Nakada
    Pages Oral6-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    (–)-Scabronines G and A, and (–)-episcabronine A, which belong to cyathane diterpenoids, were isolated from a bitter mushroom, Sarcodon scabrosus. These compounds were found to be potent stimulators of nerve growth factor (NGF) synthesis. (–)-Scabronine A has the most complex structure in the scabronine family, containing six contiguous stereogenic centers in the seven-membered ring, and (–)-scabronine G possesses the least oxidized seven-membered ring among known scabronines. We have constructed the AB-ring of scabronines via a highly stereoselective oxidative dearomatization/inverse-electron-demand Diels–Alder cascade, and have achieved the total synthesis of (–)-scabronine G in 19 steps and 21% overall yield. Inspired by the biogenesis of scabronines, the first total synthesis of (–)-scabronine A has been accomplished via a highly stereoselective oxa-Michael/protonation/acetalization cascade, and the first total synthesis of (–)-episcabronine A has also been completed via another highly stereoselective cascade.

    View full abstract
  • Tatsuya Nishimaru, Masasi Kondo, Kimito Takeshita, Keisuke Takahashi, ...
    Pages Oral7-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Marinomycin A was isolated together with marinomycin B and C by Fenical et al. from a novel marine actinomycete, Marinospora strain CNQ-140, which was cultured from a segment sample collected deep off the coast of La Jolla in California. This compound has potent antibiotic activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium.

    Marinomycin A is a unique polyene-polyol macrodiolide with an unusual 44-membered C2 symmetrical macrocycle. The monomer consists of a 2-hydroxy-6-alkenyl benzoic acid with conjugated tetraene-pentahydroxy polyketide chains containing a syn-1,3-diol as well as an anti,anti-1,3,5-triol separated by an E-alkene. Synthetic approaches to marinomycins are further complicated by their known sensitivity to light-mediated isomerization of the styrenyl alkenes, which provides an additional challenge for their selective construction. In 2006, Nicolaou et al. reported the first total synthesis of marinomycin A, followed by Evans’ second synthesis in 2012.

    We descrive here the novel total synthesis of marinomycin A by the union of epoxide 6, alkyne 7, and bromodienyl salicylic acid 8 utilizing a Suzuki-Miyaura coupling and a Mitsunobu reaction. The feature of this synthesis includes the efficient preparation of 6 and 7 from C7 cis-1,3-diol unit 5, which is easily accessible from dialkenyl carbinol 1 via Katsuki-Sharpless asymmetric epoxidation, followed by Red-Al-mediated regioselective reduction with concomitant loss of a benzyloxy group.

    View full abstract
  • Hideyuki Matsuura, Chizuru Sato, syouhei Takeichi, Kensuke Aikawa, Nao ...
    Pages Oral8-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Plants are sessile organisms and are unable to avoid environmental stresses by changing their habitats. Therefore, plants have developed unique and sophisticated defense systems. Information of local damage is transported to the distal leaves by signaling factors in order to inform biotic and abiotic stresses to the entire plant. Systemin, an 18–amino acid peptide, had been thought to be such a “mobile signal” for switching-on the plant defense system against biotic and abiotic stresses in tomato (Solanum lycopersicum). But, grafting experiments demonstrated that JA derived compound (s) rather than systemin is a component of the mobile signal for wound-induced systemic defense responses in tomato. Despite strong evidence to support JA or JA derivatives as a mobile signal, it has not been unequivocally demonstrated. We attempted to identify this unknown factor(s) and found that jasmonoyl isoleucine (JA-Ile) was the signaling factor based on the following experimental results, 1) Transient accumulation of JA-Ile in wounded and unwounded distal leaves of tomato and tobacco plants within 1 hour responded to wound stress; 2) Transportation of JA-Ile from wounded leaves to unwounded distal leaves applied under biological relevant concentration; 3) Transportation of de novo synthesized JA-Ile to unwounded distal leaves; 4) Induction of JA-mediated wound induced genes at unwounded distal leaves by supplying JA-Ile under biological relevant concentration using JA deficient mutant tomato.

    View full abstract
  • Ko Yasumoto, Mina Yasumoto-Hirose, Ryo Murata, Shun-ichi Sato, Megumi ...
    Pages Oral9-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Since the beginning of the last century, it has been known that bacteria, including cyanobacteria, are involved in the extracellular formation and precipitation of calcium carbonate (CaCO3). Such carbonate precipitation by bacteria has been observed both in vitro and in natural habitats, suggesting that this precipitation could partially contribute to the formation of marine calcareous skeletons, carbonate sediments, and deposits of carbonate in soils. Bacterial CaCO3 formation has been shown to include several pathways such as the reduction of CaSO4 to CaS by sulfate-reducing bacteria, the hydrolysis of urea leading to the formation of ammonium carbonate by urea-hydrolyzing bacteria, and the removal of CO2from a bicarbonate-containing solution by cyanobacteria and by extracellular polymeric materials such as exopolysaccharides and capsular polysaccharides isolated from Bacillus firmus and Nocardia calcarea. Despite such explanations, the mechanisms involved in the extracellular production of CaCO3by bacteria have remained largely unclear.

    It is known that CO2 at high concentrations in exhaust gases can be captured by solutions containing alkanolamine. This is called the “amine method,” which has been used since the 1930s in various industries to fix CO2gas. Recently, another synthetic amine, polyethylenimine, has been investigated as an agent for the capture of CO2 from the air. Biogenic polyamines are ubiquitous cellular components that perform multiple functions and are essential for normal growth and development. Levels of cellular polyamines are elaborately maintained at an optimum by biosynthesis, degradation, and transport. It is known that bacteria such as Escherichia. coli contain high concentrations of polyamines. For example, intracellular concentration of putrescine is approximately 20 mM while that of spermidine is about 6 mM. It is also known that biogenic long-chain polyamines do play roles in silica formation in diatoms. To our knowledge, the functional relationship between biogenic polyamines and calcification by organisms has never been reported. In this report, we examine the interaction between biogenic polyamines with CO2 and suggest roles of the polyamines in extracellular formation of CaCO3 crystals by bacteria. This new mechanism of CO2 fixation adds a novel pathway to the global carbon cycle.

    View full abstract
  • Takafumi Akimoto, Toru Nishikawa, Osamu Iwamoto, Hiroyuki Koshino, Kaz ...
    Pages PosterP-1-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    Zetekitoxin AB (ZTX) (1), one of a structural related analog of saxitoxin (STX), is a neurotoxin isolated from Ateropus. zeteki., and it shows potent inhibitory activity against voltage-dependent sodium channel. A ZTX (1) has some characteristic structures, which are tricyclic bis-guanidine structure, the same core structure as STX and its analogs, cross-linked macrolactam moiety involving isoxazolidine (at C6-C11), and N-hydroxy carbamate group on N7. Here, we described synthesis of 5 which has core structure of ZTX with quaternary stereogenic center at C11 and isoxazolidine on the side chain at C11.

    View full abstract
  • Chin Piow Wong, Jun Deguchi, Alfarius Eko Nugroho, Yusuke Hirasawa, To ...
    Pages PosterP-10-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    We have identified the Chisocheton ceramicus(Meliaceae) extracts to possess in vitroanti-adipogenesis activity on MC3T3-G2/PA6 cells. Following research led to identification of 12 limonoids, ceramicines A-L. Their relative structures were elucidated by using 1D and 2D NMR data while the absolute structure of the most potent compound, ceramicine B was determined by X-ray crystallography and CD spectrum. Nine ceramicine B derivatives (CB 1-9) were synthesized for structure-activity relationship (SAR) studies. Preliminary SAR data indicated that the C-1 carbonyl, C-2/C-3 double bond, and furan ring at C-17 were essential features for anti-adipogenesis activity. Mechanistic studies on anti-adipogenesis activity showed that ceramicine B inhibited mRNA expression and subsequently protein expression of PPARγ. Further western-blot analysis indicated that ceramicine B may play a role in the inhibition of FoxO1 phosphorylation, resulting in down-regulation of PPARγ protein and finally affecting MC3T3-G2/PA6 differentiation into adipocyte.

    View full abstract
  • Yuji Kurogome, Masaya Kogiso, Kok Kong Looi, Yasunao Hattori, Hiroyuki ...
    Pages PosterP-11-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    A number of the piperidine alkaloids, especially 2,6-disubstituted piperidin-3-ols have been found abundantly in nature and many of them show interesting pharmacological activities.

    (–)-Cassine (1) was isolated from the leaves and twigs of Cassia excelsa, and its structure was established in 1964. The absolute configuration of 1 was determined by Rice in 1966.

    While most of alkaloids generally exist as monomers, (+)-azimine (2) is macrocyclic dilactone, which was isolated from Azima tetracantha L. Structually, (+)-azimine (2) consists of two 2-methyl-3-piperidinol skeleton with a carboxyl group at the C6 side.

    In the previous report, we reported asymmetric total synthesis of (-)-cassine (1) using diastereoselective aminopalladation, however, the yield was not high enough. Therefore, we wish to report improved diastereoselective Pd(II)-catalyzed cyclization and its application to the asymmetric total syntheses of (–)-cassine (1) and (+)-azimine (2).

    View full abstract
  • Teigo Asai, Dan Luo, Sae Otsuki, Jun Nunoki, Yoshiteru Oshima
    Pages PosterP-12-
    Released: March 09, 2018
    CONFERENCE PROCEEDINGS FREE ACCESS FULL-TEXT HTML

    The epigenetic manipulation of fungal gene expression by small molecule DNA methyl transferase and/or histone deacetylase (HDAC) inhibitors influences secondary metabolism in the fungus and is an appropriate method for exploring novel fungal metabolites from cryptic biosynthetic pathways. Indeed, such chemical epigenetic method developed by us has enabled easy access for various novel skeletal natural products. However, it still remains to be investigated that what kind of fungi respond to the method well and give us structurally and biologically interesting natural products. We focused on fungi living in plants or arthropods as microbial resources for our natural product exploitation using chemical epigenetic method. When those fungi produce a variety of bioactive secondary metabolites under various stimuli derived from the interactions with their hosts, their biosynthetic gene clusters may be silenced under laboratory culture conditions. Thus, it means that they have a great potential to be a rich sources of novel natural products.

    We isolated various fungi from medicinal plants and arthropods, mainly insects and spiders. The phylogenetic tree based on their gene alignment of D1/D2 region showed that the species of isolated fungi depend on the hosts, and plants and arthropods are good sources of diverse fungi. We applied the chemical epigenetic method to the isolated fungi and found that Penicillium sp. (Catharanthus roseus), Graphiopsis chlorocephala (Paeonia lactiflora) and Mycosphaerella sp. (Aloe arborescens) enhanced the accumulation of their secondary metabolites, leading to the isolation of structurally diverse novel polyketides such as a-pyrone with bicyclo[4.2.0]octadiene (1), benzophenones with chlorine atom (6, 7 and 11), and short branched fatty acid dimers with highly substituted cyclohexenedione core (12–15). We also found that some fungi isolated from arthropods showed significantly alteration of their secondary metabolite productions by HDAC inhibitor. We therefore showed that fungi living in plants and arthropods are good sources of novel natural products by applying the chemical epigenetic method.

    View full abstract
feedback
Top