We achieved the synthesis of compound 1, which was reported as a new component of Mentha haplocalyx, and it was clarified that the proposed structure was incorrect. Next, we synthesized compound 9, whose NMR spectral data were similar to those reported for 1. However, we found that the proposed structure of 9 was incorrect again. Furthermore, we also synthesized compound 15, whose NMR spectral data were similar to those reported for 1 and 9, but its structure was found to be incorrect. Fortunately, we found that a highly polar byproduct of 15 was identical to the natural product, and then assumed that the structure would be 20 because of its polarity. Although there were two reports of isolation of cis-20 whose spectral data were similar to those of other natural products, it turned out that the correct structure of the natural products was trans-20 as a result of syntheses of both cis- and trans-20. After that, we tried asymmetric syntheses by using AD-mix through two routes (A and B) and obtained both (+)- and (-)-trans-20. To our surprise, it was found that either of route A or B is against to the general rule of AD-mix. To determine the absolute configuration, we transformed (+)-trans-20 into 22 by hydrogenation and confirmed the agreement with 22 from (-)-terpineol, so we achieved the determination of the absolute configuration of trans-20.

抄録全体を表示

(+)-Vibsanin A (1) was isolated from Viburnum odoratissimum by Kawazu in 1980. This natural product showed piscicidal activity. The structure of 1 is characterized by an 11-membered ring skeleton containing an all-carbon asymmetric quaternary stereocenter. Interested in the unique structure, we have involved in synthetic study of 1. We first synthesized the upper-half segment 4. 4-Pentyn-l-y1 acetate (7) was converted to aldehyde 12, which was subjected to olefination using the Ando reagent to provide (Z)-α,β-unsaturated ester 13. The reduction of 13, followed by the Sharpless asymmetric epoxidation of the resultant allylic alcohol 6, provided epoxy-alcohol 14 in 97% ee. The alcohol 14 was oxidized to aldehyde 4. The coupling reaction of 4 and the model lower-half segment 15 afforded 16-A and 16-B, which were converted to iodoalkene-aldehyde 19. The intramolecular Nozaki-Hiyama-Kishi reaction of 19 proceeded smoothly, giving the cyclized product 20. The isomerization of the exo-olefin in 20 occurred under the Mitsunobu condition to result in the formation of an undecadiene skeleton. The selective removal of the p-nitrobenzoyl group in 21 furnished 22, the norprenyl analogue of 1. We next developed a stereoselective synthesis of the all-carbon quaternary stereocenter through zinc-mediated Barbier-type allylation of sugar-derived aldehyde 23 with allylic chloride 9. The major isomer 24 was converted to alcohol 26 via hydroboration-oxidation. Further synthetic endeavor toward the total synthesis of 1 is in progress.

抄録全体を表示

TBMB acid (1) was designed by Ohrui and co-workers and found to be useful for a chiral strong fluorescent agent. The racemic mixture of acetal 2a was resolved with C. antarctica lipase B-mediated remote-controlled transesterfication. These diastereomerically pure (2R,1'5)-2a and (2S, 1 'S)-2b were led to both enantiomers of TBMB acid (1). This chiral acetal would be a potential chiral synthon for synthesis of natural product. Carnosic acid (3) was isolated from rosemary, Rosmarinus officinalis by Wenkert and co-workers. Sato and co-workers reported that carnosic acid (3) protects neuronal cell via activation of keap 1/Nrf2 pathway. This trans-decalin skeleton was planned to be constructed by stereoselective domino cyclization of the acyclic precursor 5. This stereoselectivity would be controlled by steric repulsion between t-Bu group on chiral acetal and the substituent R. The domino cyclization of 13a afforded only undesired regioisomer. It would arise from coordination of the hydroxy group to the carbocation intermediate. However, benzyl ether 13b and hydrophobic isopropyl group substituted 13c did not provide the desired regioisomer. α-Iodination of α,β-unsaturated lactone 17 gave iodide 18. Reduction and subsequent acetalization afforded ethyl acetal 19. Kumada coupling of acetal 19 with bromide 20 gave adduct 21 in good yield. Resulting coupling product 21 was deprotected and subsequent Luche reduction produced diol 22. Diol 22 was transformed as bismesylate. Allyl mesylate was selectively substituted to acetate with cesium acetate. Acetyl group was removed and the alcohol 24 was protected with TIPS group. Substitution of mesylate to bromide gave trans-decalin skeletal carbon 25. Suzuki-Miyaura cross-coupling of bromide 25 with aromatic compounds was investigated. Coupling of iodoester and 25 gave desired product in moderate yield along with undesired homo-coupling product 32. PPh_3 ligand was found to be suitable for suppression of generation of 32. Improvement of yield of cross-coupling and subsequent domino cyclization are now in progress.

抄録全体を表示

Zeylanone (1) was isolated from Plumbago zeylanica in 1979 by Sankaram et al. This compound shows cytotoxic actives against cancer cell lines, antibacterial, and antifungal activity. The structurally related dimeric naphthoquinones, juglocombin A (2) and juglorescein (3) were isolated from Streptomyces sp. 815 and GW4184, respectively. Although the structures of 1, 2, and 3 were comfirmed by detailed NMR studies, the relative and absolute configurations of these compounds have not been determined. It has been proposed that 1 would be biogenetically synthesized by dimerization of plumbagin (4). The sequential intermolecular and intramolecular Michael reactions of 4, followed by oxidation of the resulting hydroquinone would give 1. We report herein the first synthesis of 1 based on the proposed biosynthetic pathway as well as the determination of the stereochemistry of 1. Vitamin K_3 (5) was used as a model substrate to develop the key dimerization. We found that treatment of 5 with sodium hydroxide in ethanol under an aerobic atmosphere afforded a dimeric epoxide 8 in 37% yield. The structure of 8 was comfirmed by X-ray crystallography. The cis relationship between the methyl group at C-5a and H-12a, and the anti relationship between the methyl group and the epoxide were indicated. The formation of 8 would be explained by formation of the dianion species 10 and subsequent epoxidation with molecular oxygen. Using the key dimerization, we have accomplished the synthesis of zeylanone (1) starting from 4. Compound 4 was converted into the methoxy methyl ether 11. Dimerization of 11 with KOH in CH_2Cl_2-MeOH under an oxygen atmosphere afforded the dimer 12 in 63% yield. Treatment of 12 with potassium iodide in acetic acid, followed by p-toluenesulfonic acid gave 1 in 78% yield in 2 steps. The 11-1 NMR spectrum for synthetic 1 was in agreement with that reported for natural 1. According to the X-ray structure of 8, the cis relationship between the methyl group at C-5a and H-12a was established in 1. Furthermore, we prepared the key intermediate 21 for the synthesis of juglocombin A (2) and juglorescein (3), utilizing the key dimerization of 1,4-naphthoquinone 20.

抄録全体を表示

To develop more potent α-glucosidase inhibitors whose seed-compound is salacinol (1), a potent natural α-glucosidase inhibitor isolated from Salacia reticulata of Ayurvedic traditional medicine, a series of 3'-O-benzylated analogs of 1 were designed with the aid of in silico method. Intensive docking studies proposed several promising compounds. To verify the computational SAR assessments, designed derivatives were synthesized and evaluated in vitro. Their α-glucosidase inhibitory activities against rat intestinal α-glucosidases were so potent as were expected by the docking studies, and all the compounds showed superior inhibitory activities to the original sulfonium sulfate (1). Among the sulfonium salts designed, one with 3'-O-(ortho-nitrobenzyl) moiety (8k) was found to be the most potent, and ca. forty times as potent as 1, the compound being the strongest inhibitor among the sulfonium type inhibitors synthesized so far. [chemical formula]

抄録全体を表示

In 2002, Shin-ya and his coworkers isolated versipelostatin(VST) A from the culture broth of Streptomyces versipellis and identified it as a down-regulator if grp78 gene expression. VST A consists of trisaccharide attached to a seventeen-membered macrocycle fused to spirotetronate and octalin units. Our interest in the its structural features and biological activity led us to pursue to its synthesis. In this study, we achieved syntheses of the both of spirotetronate unit and C-3-C-10 unit of VST. At first, the spirotetronate unit was synthesized via construction of stereoselective tetronate core installation and quarterly center by Johnson-Claisen rearrangement from optically active pulegone as a starting material. The C-3-C-10 unit was synthesized from hydroxymethylpropionate via asymmetric aldol reaction, stereoselective reduction and C4 elongation by Wittig reaction. Each of these protocol need ten or eleven steps, and provide good overall yields. We also succeeded in the anion-mediated coupling reaction of these units. Further synthetic studies toward the total synthesis of versipelostatin A are now in progress. [chemical formula]

抄録全体を表示

Horner-Wadsworth-Emmons reaction (HWE reaction) is known as a reliable and powerful method for carbon-carbon bond formation by coupling between β-ketophosphonate and aldehyde to give α,β-unsaturated compound with high stereoselectivity. In general, the β-ketophosphonate used as the HWE reaction precursor is needed to be synthesized from a readily accessible material. However, these procedures sometimes encounter troubles in purification due to its high polarity or side products. To avoid these problems, we planned one-pot synthesis of the α,β-unsaturated ketone with aldehyde, acyl fluoride and trimethylsilylmethylphosphonate through HWE reaction according to the sequential reaction illustrated in Scheme 1. The reaction conditions were optimized by examining bases, reaction time, and equivalent of reagents as shown in Table 1. With the optimized conditions (Table 1. Entry 7), wide variety of substrates (aldehyde, acyl fluoride, and phosphonate) bearing various functional groups were coupled to give α,β-unsaturated ketone in high yields with E geometry. (Table 2) Z-α,β-Unsaturated ketones were also prepared with high stereoselectivity by using one-pot procedure. (Table 3)

抄録全体を表示

1. Synthesis of prodelphinidin B3 (1). Stereoselective synthesis of prodelphinidin B3 (1) was achieved using Yb(OTf)_3 mediated equimolar condensation of catechin nucleophile and gallocatechin electrophile. The coupled product was successfully converted to prodelphinidin B3 (1). 2. Synthesis of prodelphinidin C2 (2). Stereoselective synthesis of prodelphinidin C2 (2) was achieved using AgOTf mediated equimolar condensation of gallocatechin-catechin nucleophile and gallocatechin electrophile. The condensed product was successfully converted to prodelphinidin C2 (2). 3. Antitumor activity against prostatic carcinoma Synthesized prodelphinidin B3 (1) and prodelphinidin C2 (2) were investigated antitumor effect againt prostatic carcinoma using cell count method. Prodelphinidin B3 (1) showed significant antitumoral effect. The activity was almost same as EGCG. With regards to the prodelphinidin C2 (2), the activity was weaker than that of prodelphinidin B3 (1).

抄録全体を表示

Because prodrugs ,procosumetics and prosupplements (precursors of drugs, cosmetics and dietary supplements that are metabolized within the body to form the corresponding bioactive materials) have recently attracted a great deal of attention, there is a growing need for techniques that are capable of selective chemical modification of functional compounds. I have focused on glycosylation, particularly glycosylation, as one such type of chemical modification. There have been many studies on the production of useful substances by organic syntheses through routes that incorporate reactions induced by biocatalysts, such as cultured cells or enzymes, and the results of such studies have been applied in the production of a range of fine chemicals, including pharmaceuticals, aroma chemicals, and food additives. Among the biocatalysts that have been used are microorganisms, fungi, yeasts, animal cells, and enzymes extracted from these sources. In addition, biotransformations effected by using cultured plant cells as biocatalysts have recently attracted attention. Plants, which live on land and are generally incapable of movement, produce various secondary metabolites for the purposes of self-defense and signal transduction. As a result, plant cells contain a range of enzymes that have inherent abilities to transform or to synthesize organic substances. With the aim of utilizing the intrinsic ability of plant enzymes to effect biotransformations, we have studied biotransformations of exogenous substances (biological compounds) by cultured plant cells and I have succeeded in effecting a range of reactions, including reduction, hydrolysis, isomerization, glycosylation, esterification, and hydroxylation reactions, by using cultured plant cells as biocatalysts. Glycosylation by plant cells is a particularly important reaction that is involved in the activation of metabolites in cells and might, therefore, be useful in stabilizing various biologically active compounds or in activating various physiological functions. Here we repot the results of our studies to date on the biotransformation and functional activity of bioactive compounds.

抄録全体を表示

The proanthocyanidins (condensed tannins or oligomeric flavonoids) are known to be extremely strong antioxidants: investigating them has become increasingly important because of various strong bioactivities. These compounds exist in many edible plants, fruits, cocoa, chocolate, tea, etc. In many cases, however, proanthocyanidins are obtained as a mixture of various analogues, making purification of each compound so difficult. So we have developed and reported a simple, versatile, and completely stereoselective method of synthesizing proanthocyanidin oligomers and we used them for biological assays. We report here new synthesis methods of dimers using TBDMS protected nucleophiles derived from (+)-catechin or (-)-epicatechin and acetylated electrophiles derived from flavan-3-ol peracetates. Condensation studies of TBDMS protected nucleophile with benzylated electrophile in the presence of several Lewis acids were examined. Surprisingly, in the case of using TMSOTf as catalyst, one of the TBDMS groups of the D-ring was removed selectively. Furthermore, condensation of acetylated electrophiles with 1 eq. nucleophile gave oligomers in good yield. Various biological assays and chemical biology studies are now underway.

抄録全体を表示

We describe the synthesis of lagerstannin (1), the synthesis of the reported structure of roxbin B (2), revision of the reported structure, and the synthesis of revised roxbin B (3). Each compound has been synthesized for the first time. [chemical formula] In the synthesis of 1, highly diastereoselective construction of the 4,6-hexahydroxydiphenoyl (HHDP)-bridge and adoption of the benzyl ester as the protecting group of the carboxylic acid were essential. For the formation of the 4,6-HHDP-bridge, intramolecular aryl-aryl coupling of two 4-O-benzylated gallates on the 4,6-positions of D-glucose was applied.5 The adoption of the benzyl ester facilitated the final deprotection and purification. In the synthesis of 2, axially chiral HHDP-diacid and the corresponding acid anhydride were utilized to prepare the HHDP-bridges at the 4,6- and 1,2-positions, respectively. The synthetic 2 was different from natural roxbin B. Reconsideration of its structure suggested two candidates as the revised structure, which were 1-O-galloy1-2,3-O-(R)-HHDP-4,6-O-(S)-HHDP-β-D-glucose (3, reported as cuspinin) and 3-O-galloy1-1,2-O-(R)-HHDP-4,6-O-(5)-HHDP-β-D-glucose (19). The syntheses of these compounds revealed that the structure of roxbin B was 3, which is identical to cuspinin.

抄録全体を表示

Ellagitannins are polyphenolic natural products with a wide range of biological activities and remarkable structural diversity. In this class of polyphenolics, rugosin B and isorugosin B possess a unique part structure called valoneoyl group, which is generated by a C-C/C-O oxidative coupling of galloyl groups in plants. Although, during the last two decades, a number of chemists have challenged to synthesize ellagitannins, there is no example of the synthesis of valoneoyl-containing ellagitannin. In this context, we attempted to synthesize rugosin B and isorugosin B. Generally, there are two strategies for the synthesis of ellagitannin. We adopted Route B, thus the synthesis was commenced with construction of valoneoyl moiety. Enantioselective construction of the axially chiral biaryl function was achieved by the Pd-catalyzed intramolecular biaryl coupling reaction of 10 and the atroposelective lactone opening reaction of 11. As a result, the key intermediate 15 was obtained in an enantiomerically pure form. Carboxylic acid 15 was condensed with sugars 16 and 19 to afford methylated rugosin B (18) and isorugosin B (21) respectively. All attempts for the cleavage of the phenolic methyl ethers were unsuccessful. The practical method to construct the biaryl ether moiety protected by the benzyl groups, which is essential for the total synthesis of ellagitannins, will be also discussed.

抄録全体を表示

Vizantine (3) is a synthetic derivative of treharose-6,6-dicorynomycolate (TDCM) which was characterized in 1993 as the cell surface glycolipid of Corynebacterium diphtheriae and shows a variety of significant biological activities for adjuvant development. In vitro, vizantine activates not only the macrophages of mice sera, but also induces the release of MIP-1β, IL-6, IL-8 etc. from human acute monocytic leukemia cell line cells (THP-1 cells). Because almost no TNF-α is induced in vivo, the lethal toxicity to animals was found to be ncredibly low. However, oral administration of vizantine to C57BL/6 mouse (p.o. 100 μg x 7 times) inhibits lung metastasis of B16-BL6 melanoma cells (which are classified in highly metastatic tumor cell). In recent years, structural components of the outer surface membrane of bacteria have attracted considerable attention as lead compounds for adjuvant development. However, a concern of the use of these compounds is that they can over-activate innate immune responses leading to the clinical symptoms of septic shock. Therefore, an important issue is a detailed knowledge of the immunostimulatory mechanism to harness beneficial effects without causing toxicity. Here, to advance the mechanistic studies of vizantine, we have synthesized magnetic beads-attached 4 that maintain immunological activities and can therefore act as a molecular probe. Using a pull-down assay of 4 and the extract of HEK-293T cells transfected with plasmid for TLR4 and MD2, vizantine was found to act as a ligand of the Toll-like receptor 4 (TLR4) and MD2 complex. Furthermore, the macrophage from TLR4 knockout (TLR4 -/-) mice showed decreased response to vizantine, but that from TLR2 knockout (TLR2 -/-) mice did not. Taken together the results suggest that vizantine suppresses the tumor lung metastasis through the activation of macrophages via TLR4/MD2 complex.

抄録全体を表示

In 2002, pyrrocidine A and B were isolated from the fermentation broth of a fungus, LL-Cyan 426, as antimicrobial agents against Gram-positive bacteria including drug-resistant strains. Structural features of pyrrocidines are tricyclic decahydrofluorene core (ABC-ring) and 13-membered macrocycle containing para-substituted aryl ether moiety. The complex molecular architecture of these compounds makes them very attractive target molecules for total synthesis. We report herein the stereoselective synthesis of decahydrofluorene 21 which provides the first entry to the ABC-ring moiety of pyrrocidines. The synthesis of 21 commenced with the construction of the C-ring moiety. The cyclic carbon skeleton was synthesized via Diels-Alder reaction between dimethyl-substituted Danishefsky-Yan diene 7 and trisubstituted alkene 8 to afford a diastereomeric mixture of cyclohexenone 10a-b. The ketone 11a possessing the desired configuration was mainly obtained by thermal epimerization of the diastereomeric mixture of 11a-c. Ring-closing metathesis reaction of diene 15, followed by Dess-Martin oxidation afforded the cyclic dienophile 16. Diels-Alder reaction between Danishefsky-Kitahara diene 5 and bicycloenone 16, and the sequential acidic treatment gave diketone 4, establishing the tricyclic carbon framework of 21. Owing to the inherent convex-face selectivity of cis-fused bicyclic AB-ring moiety of 4, nitrile 19 was stereoselectively synthesized in several steps. Vinyl group was introduced to 4 from concave face selectively, avoiding the adjacent cyano group, in two steps to afford ketone 20. The reduction of ketone group from convex face of 20, followed by Chugaev elimination furnished decahydrofluorene 21.

抄録全体を表示

Nigricanocide A dimethyl ester (1), which originated from the green alga Avrainvillea nigricans, is an antimitotic galactoglycerolipid. It is structurally characterized by two ether linkages between a galactosyl glycerol and a C20 oxylipin and between C16 and C20 oxylipins. While the planar structure of the lipid chains and the partial relative configuration of the galactosyl glycerol moiety have been determined, the full absolute stereochemistry is unclear. Therefore, we started a program for determining the full absolute stereostructure of nigricanoside A dimethyl ester by total synthesis. As a part of the program, stereoselective methods for constructing the ether linkages between the galactosyl glycerol and the C20 lipid chain and between the C20 and C16 lipid chains have been developed. Model compounds ((8'R)-4 and (8'S)-4) corresponding to the bottom half of 1, including the C20 lipid chain and the galactosyl glycerol, has also been synthesized. The ether linkage between the galactose and the C20 lipid chain was constructed stereoselectively by the chirality-transferring Ireland-Claisen rearrangement of a 1-substituted-2-bromoallyl alkoxyacetate, which consisted of an optically active 2-bromo-1-alken-3-ol and a 6-(carboxymethoxy)galactose derivative. The rearrangement products were converted to model conpounds (8'R)-4 and (8'S)-4 via a process including Julia olefination with sulfone 5, Mori's alkyne formation, and Lindlar hydrogenation. The ether linkage between lipid chains was stereoselectively synthesized by an Evans type aldol reaction under lithium enolate conditions. Details will be presented in the poster session.

抄録全体を表示

JBIR-23 and -24 (1,2), isolated from culture broth of Streptomyces sp. AK-AB27, were reported by Shin-ya and co-workers in 2009. These natural products have potent activity against malignant pleural mesothelioma (MPM) cells. The structure of 1 and 2 are characterized by a dodecahydrodibenzo[b,d]furan skeleton bearing a unsaturated side chain. Here we present a synthetic approach toward 1 and 2 using double Michael addition as a key step. First, enone 6 was synthesized in 6 steps from 1,4-cyclohexanediol (9). Mukaiyama-Michael reaction between the enone 6 and silyl enol ether 16, which was obtained from conjugated addition of vinylcuprate 8 and cyclohexenone (7), afforded the diketone 17 and subsequent manipulations gave the tricyclic ketone 5. Then, the ketone 5 was converted into the allylic alcohol 21 via i) silyl enolization with LDA and TMSC1, ii) oxidation with IBX and NMO, and iii) DIBAL-H reduction. Further studies toward the total synthesis of JBIR-23 and -24 are in progress.

抄録全体を表示

Organocatalytic asymmetric transformations have recently attracted a great deal of attention from synthetic chemists as powerful and fascinating tools because of their mildness, high efficiencies, and environmentally friendly characteristics. In this laboratory, we have been interested in the use of this technique for the synthesis of biologically interesting natural products in optically active forms. In this presentation, our own synthetic approaches to biologically interesting natural products using organocatalytic asymmetric transformations will be discussed. The major topics are as follows: 1. Chiral diamine-catalyzed Robinson-type annulation: we have developed an unprecedented organocatalytic asymmetric synthesis of cyclohexenone derivatives with a quaternary carbon stereogenic center at the 4-position with complete control via chiral diamine/dicarboxylic acid-catalyzed Robinson-type annulation. 2. Formal synthesis of (+)-sporochnol A: the above methodology was successfully applied to the short synthesis of (+)-sporochnol A. 3. Formal synthesis of (-)-mesembrine: a new short synthesis of (-)-mesembrine was also achieved using the same synthetic strategy as above. 4. A practical synthesis of aminohydroxyacetone synthons: a new practical method for the synthesis of aminohydroxyacetone synthons has been developed, and their versatile utility in organocatalytic asymmetric aldol and Mannich reactions was exemplified by using a pyrrolidine-tetrazole organocatalyst. 5. Asymmetric synthesis of aza-sugars: the great utility of aminohydroxyacetone synthons obtained above was demonstrated by the short-cut synthesis of aza-sugars in an enantioselective manner.

抄録全体を表示

Reidispongiolide A (1) was isolated from the New Caledonian sponge Reidispongia coerulea. Reidispongiolide A (1) was revealed to demonstrate antimicrofilament activity and to inhibit the growth of multidrug-resistant (MDR) cancer cell lines. Its absolute configuration was established in 2005 by X-ray crystal structure analysis of the compound bound to actin. To investigate structure-activity relationships and biological activities of reidispongiolide A, we began to synthesize reidispongiolide A. Firstly, the C1-C3 segment (4) and the C4-C22 aldehyde (2), containing seven asymmetric centers, and C23-C35 sulfone (3), containing seven asymmetric centers were synthesized. Secondly, C4-C22 (2) and C23-C35 segments (3) were connected by using an intermolecular Julia coupling reaction. Thirdly, an intermolecular Stille coupling reaction was employed for the union of the C1-C3 (4) and C4-C35 segments. For the synthesis of C4-C22 segment (2), C4-C10 alkyne (7) and C11-C22 aldehyde (6) were synthesized. The synthesis of C11-C22 aldehyde (6) was carried out by using a Horner-Wadsworth-Emmons reaction between C11-C16 phosphonate (8) and C17-C22 aldehyde (9) as a key step.. The synthesis of C23-C35 sulfone (5) was carried out by using a Horner-Wadsworth-Emmons reaction between C23-C29 aldehyde (14) and C30-C35 phosphonate (13). Chiral centers of (5) was introduced by using a Paterson aldol reaction, stereoslective reduction of β-hydroxy enone, and crotylboration as the key steps. C4-C22 segment (2) and C23-C35 segments (3) were connected by using an intermolecular Julia coupling reaction. The synthesis of C1-C35 segment (33) was carried out by using an intermolecular Stille coupling reaction between C4-C35 segment (32) and C1-C3 segment (4). Finaly we achieved the deprotection of C1-C35 segment (33) and macrolactonization by using a Shiina protocol.

抄録全体を表示

18E-Lyngbyaloside C (1), a 14-membered glycosidic macrolide isolated from the marine cyanobacterium Lyngbya bouilloni, has been shown to exhibit cytotoxicity to HeLa cell lines. We previously reported that Rh_2(S-BPTPI)_4 is a highly effective Lewis acid catalyst for endo- and enantioselective hetero-Diels-Alder (HDA) reactions of a diverse range of aldehydes with Danishefsky-type and Rawal's dienes, in which enantioselectivities up to 99% ee have been achieved. In order to demonstrate the utility of this catalytic process, we embarked on the total synthesis of 1. The synthesis of the C1-C8 fragment 9 was initiated with the HDA reaction between Danishefsky-type diene 3a and benzyloxyacetoaldehyde (14) in the presence of 1 mol% of Rh_2(R-BPTPI)_4 to provide dihydropyranone 13 in 83% yield with 91% ee. The Mukaiyama-Michael addition reaction of silyl ketene acetal derived from ethyl acetate to 13 followed by Ito-Saegusa oxidation gave 2,6-disubstituted dihydropyranone 12, which was converted to tetrahydropyran 19. Removal of the benzyl ether followed by incorporation of the thiotetrazole via the Mitsunobu protocol and oxidation of the derived sulfide furnished sulfone 9. The HDA reaction between Rawal's diene (6) and (R)-3-(4-methoxybenzyloxy)-2-methylpropanal (17b) under catalysis by 1 mol% of Rh_2(R-BPTPI)_4 proceeded cleanly and gave, after treatment with acetyl chloride, the desired dihydropyranone 16b in 82% yield with 95:5 diastereoselectivity. Treatment of 16b with MeLi followed by oxidative rearrangement, stereoselective epoxidation and reduction of epoxylactone provided triol 25, which was uneventfully converted to tosylate 26. Cyanide displacement of the O-tosyl group followed by a sequential reduction with DIBAL-H and NaBH_4 furnished alcohol 27. Protection of the C16 hydroxy group as its MEM ether was followed by oxidative removal of the MPM group and Dess-Martin oxidation to produce the C9-C16 fragment 10. A Julia-Kocienski olefination between the C1-C8 fragment 9 and the C9-C16 fragment 10 afforded E-alkene 8. Sequential catalytic hydrogenation of the double bond and cleavage of the benzylidene protecting group furnished diol 28. Further efforts toward the total synthesis of 1 are currently underway.

抄録全体を表示

[Background] In 1989, Isono and co-workers reported the isolation of tautomycetin (TC, 1), which had potent activity against Sclerotina sclerotirum, from a culture of soil acitinomycete, Streptmyces griseochromogenes. Later, the antibiotic was found to induce the morphological change (bleb formation) of human leukemia cells K562, and affect to the production of secondary metabolites in Penicillium urtcae. It was revealed that TC is a specific inhibitor of serine/threonine protein phosphatase 1 (PP1). Here, we report synthetic study of four segments of TC and its analog demethyl phenyl tautomycetin. [Optimization of boron aldol reaction] In the course of our synthetic study of TC, we planed to use borone aldol reaction as a key reaction. First we attempted to synthesize model compounds (8 and 9) for optimization of aldol reaction conditions to obtain the aldol adducts with high yield and diastereometric excess (Scheme 2). The desired aldol adduct (17) was obtained in 96%yield and 90%de by DIPOTf mediated enolization for 30min at -78℃ and then for lh at 0℃ (Table2, entry2). [Synthesis of each segment] Segment A: We completed synthesis of Segment A from acetylene dicarboxylic acid dimethyl ester (18) in 8 steps including two key reactions, regioselective nucleophilic addition reaction and asymmetric reduction by (+)-DIPCl (70%ee) (Scheme 3). Segment B and C: Segment B and C were effectively led from the key compound (25) that resembles the model compound (8) of aldol reaction (Scheme 4). Segment D: Chiral dicarboxylic acid was converted into bromide (30) in good yield. And Weinreb amide (34) as another fragment was synthesized from methyl chloroformate (31) in 3steps and 45% overall yield (Scheme 5). Segment D': Bromide(37) was easily obtained from commercially available acetate(35). The organolithium compound generated from 37 was condensed with benzaldehyde to give alcohol (38). TES protection of 38 followed by ozonolysis afforded Segment D' (7)(Scheme 6). Thus we have developed synthetic routes to four segments of TC. The coupling of each segments are under way using Mistunobu reaction and Honor-Emmons reaction.

抄録全体を表示

Microbial species have a capability to produce a wide variety of bioactive compounds with novel structures and various biological activities. In our continuing studies on secondary metabolites from Streptomyces sp., we have been much interested in the bis/tri/tetra-lactone antibiotics with 3-formamidosalicylic or 3-hydroxy-4-methoxypicolinic moieties. A marine-derived Streptomyces sp. produced splenocin B (1), which has similarity to UK-2A and antimycin A_<3b> (AA) in structure and displays potent suppression of cytokine production in ranges from low micromolar to low nanomolar and exhibits minimal mammalian cell cytotoxity. Herein, we like to report our preliminary studies on the synthesis of splenocin B. Our synthetic strategy of 1 involves 1) Kita-Fujioka lactonization via ethylvinyl ester and 2) intramolecular Mitsunobu reaction for the construction of the 9-membered bislactone moiety. The cyclization precursors 4 and 5 were prepared from the corresponding β,γ-dihydroxycarboxylic acid, obtained by asymmetric Evans aldol reaction, and L-threonine / allo-L-threonine derivatives. The key cyclization reactions proceeded smoothly to construct the strained nine-membered ring framework of splenocin B in modest yields. Further approach to splenocin B is currently underway and will be reported.

抄録全体を表示

Recently, many α-amino acid analogs (AAA) in which the carboxyl group of α-amino acids is replaced with other acidic functional groups, e.g., sulfinic acid, sulfonic acid, phosphinic acid, phosphonic acid, boronic acid, and tetrazole, have been developed. Incorporation of these AAAs into biologically active peptides has received significant attention from bioorganic and medicinal chemists. We have recently developed α-amino squaric acid (-ASQ)bearing a 4-hydroxy-2,3-dioxocyclobut-1 -enyl (SQ) group as a carboxylic acid surrogate of amino acids. The SQ group is characterized by its planar structure, acidic OH group, and electron deficient property, and widely employed as a potent carboxylic acid surrogate in medicinal chemistry. These chemical properties prompted us to investigate the synthesis of new α-ASQ-containing peptides. We will report the synthesis of novel α-ASQ-containing peptides in liquid phase and the construction of the peptide library by solid phase synthesis. Conformational analysis and preliminary biological evaluation of these peptides will be discussed.

抄録全体を表示

Dibromophakellin (1) and its related compounds of (+)-dibromophakellstatin (2) and (+)-cylindradine A (3) are known to a member of pyrrole-imidazole marine alkaloids. In spite of their structural similarities, these families show variety of biological activities. In addition, these compounds possess a characteristic fused-type tetracyclic skeleton that contains cyclic guanidine or urea moieties with chiral vicinal aminal, thus, they are attracted as synthetic targets. In this paper, we will describe total synthesis of (+)-dibromophakellin (1) and (+)-dibromophakellstatin (2). We also discuss about our synthetic efforts for (+)-cylindradine A (3). In our synthesis of (+)-dibromophakellin (1) and (+)-dibromophakellstatin (2), we applied the Overman rearrangement reaction for constructing N,N-aminal center at C10 with transfer the chirality at C12 of allylic alcohol 14 (Scheme 3, 14→46). Based upon this strategy, we achieved total synthesis of 1 and 2, respectively. For the synthesis of (+)-cylindradine A (3), we tried to apply the same strategy of 1 and 2 for constructing N,N-aminal center at C10, however, we could not access to the precursor for the Overman rearrangement. Therefore, we adopted the intramolecular oxidative cyclization reaction of guanidine 40 for constructing the N,N-aminal center. Reaction of 40 with hypervalent iodine (PhI(OAc)_2) took place, and tetracyclic ring system was constructed via iminium cation 41 to form 42 in 60% (Scheme 9, 40→42). Further synthetic studies toward (+)-cylindradine A (3) are in progress.

抄録全体を表示

A number of isoquinoline alkaloids exist in nature. Due to their unique structural motifs with an interesting biological activities the synthesis of isoquinoline alkaloids have attracted much attention for many years. Particularly, many of tetrahydroisoquinoline alkaloids possess chiral center at C-1 carbon, and both R- and S-carbon centers are found widely in nature. Therefore, an asymmetric construction of the chiral center is an important task for their syntheses. We have developed a Pd-catalyzed intramolecular cyclization of ζ-amino-α,β-unsaturated chiral alcohol via 1,3-chirality transfer. Although PdCl_2 catalyst did not provide satisfactory results for the synthesis of 1-alkenyl tetrahydroisoquinoline from N-Boc protected (S,E)-4-[2-(2-aminoethyl)phenyl]but-3-en-2-ol, we have found some suitable catalysts such as Bi(OTf)_3, Fe(OTf)_3, methyl trifluoromethane-sulfonate and dimethyl sulfate efficiently working on this synthesis. In this paper, we describe the detail of sulfonate ester catalyzed 1,3-chirality transfer for the synthesis of 1-alkenyl-tetrahydroisoquinoline and total synthesis of tetrahydroisoquinoline alkaloids including (+)-dysoxyline and (+)-colchi-ethanamine. Though the carbon extension of C-1 chain by the route via Wittig olefination gave (+)-dysoxyline with partially racemization, by that via Julia-Kocienski olefination provided (+)-disoxyline and (+)-colchiethanamine without racemization. For the synthesis of tetrahydro-pβ-carboline, protecting group on the nitrogen of indole ring is critical for the chirality transfer. When Tf group was used on it, its strong nature of electron withdrawing property conducted the cyclization to give a chiral 1-alkenyl tetrahydro-β-carboline with a 75 : 25 enantiomeric ratio.

抄録全体を表示

Colchicine (1) is a well-known bioactive alkaloid that is used for the therapy of acute gout. It also acts as an antimitotic agent by binding to tubulin. However, practical anti-cancer medicines derived from colchicines have not been developed so far because of their toxicity to normal cells. In the present study, a series of novel colchicine derivatives possessing various substituents at C-4 position were prepared from colchicine (1). Among them, 4-halocolchicines 3-6 were found to exhibit more potent cytotoxicity to the tumor cells (A549, HT29, HCT116) than 1. Evaluation of the cell-growth inhibitory activities of 4-fluorocolchicine (3) and 4-chlorocolchicine (4) using mice transplanted with the HCT116 human colorectal carcinoma cell line by intraperitoneal injection demonstrated that they are capable of reducing the intrinsic toxicity of colchicine (1) and show potential for use as a clinical drug. We designed safer and more effective antitumor agents based on a tumor-activated pro-drug strategy that involved the release of free drug by the action of cathepsin B, an enzyme overexpressed in tumor cells. We prepared pro-drug 13 which consist of three parts: 4-fluorodeacetylcolchicine (12) as the active drug that would be generated by the action of cathepsin B; the lysosomally cleavable dipeptide Phe-Lys; and the self-immolative p-aminobenzyloxycarbonyl spacer between the active drug and the dipeptide. We confirmed that pro-drug 13 released the active drug 12 via the action of cathepsin B. Pro-drug 13 exhibited an approximately two-fold higher selectivity for tumor cells than normal cells. We next designed double pro-drug 21 that was activated first by nitroreductase under hypoxia, which is a common characteristic of solid tumors, to generate pro-drug 22 and then by cathepsin B to generate the active drug 23. Double pro-drug 21 was prepared by the coupling of dipeptide 36 with N-Boc colchicine derivative 37. Biological evaluation of double pro-drug 21 is currently underway.

抄録全体を表示

Hypervalent iodine reagents are useful synthetic tools due to their low toxicity, ready availability, and easy handling. In our previous works, we developed an electrochemically generated hypervalent iodine, PIFE [phenyliodine(II)bis(trifluoroethoxide)], which possesses comparable or superior properties to that of commercially available hypervalent iodine oxidants, PIFA [phenyliodine(II)bis(trifluoroacetate)]. Its availability was demonstrated by construction of quinolinone skeletons. This methodology was employed as a key step for the synthesis of the bioactive tetrahydropyrroloiminoquinones and carbazoles natural products, including makaluvamines, damiron and glycozoline. The quinolinone construction by PIFE smoothly underwent in moderate yield. On the other hand, the carbazole construction by PIFE was accomplished in higher yield than the use of PIFA as an oxidant. In addition, we employed PIDA [phenyliodine(II)diacetate)] as a key step for synthesis of cyclotryptamine alkaloids including debromoflustraminol B and CPC-1. The cyclotryptamine construction by PIDA and addition of NaOAc smoothly underwent in moderate yield. In this presentation, the details of our research will be discussed.

抄録全体を表示

(+)- Pancratistatin (1) and (+)-trans-dihydronarciclasine (2) are Amaryllidaceae alkaloids, which have potent antitumor activities. Both 1 and 2 were isolated by Pettit et al from the bulbs of Hawaiian Hymenocallis littoralis in 1984 and Chinese medicinal plant Zephyranthes candida in 1990 respectively (Figure 1). These natural products are challenging synthetic targets because of its structural complexity that includes highly oxygenated phenanthridinone core with successive stereogenic centers on the cyclohexane ring. The first total synthesis of racemic 1 was reported by Danishefsky et al in 1989. Six years later, the asymmetric total synthesis was developed by Trost et al. Although, many total syntheses of 1 have been reported to date, only one asymmetric synthesis of 2 has been reported by Studer et al in 2008. We have recently succeeded in the asymmetric total synthesis of another Amaryllidaceae alkaloid (-)-lycorine (3) by using asymmetric conjugate addition cascade of α,ω-dialkenoate. As our continuous study on asymmetric total synthesis of this class of alkaloids, we described herein the total synthesis of (+)-trans-dihydronarciclasine (2) using chiral ligand-controlled asymmetric conjugate addition as key step. An asymmetric conjugate addition of aryllithium 6, generated from the corresponding arylbromide and butyllithium at -78℃, was performed with enoate 7 using tridentate chiral ligand 9a in toluene at -78℃ for 1.5 h to afford a 92:8 mixture of cis-adduct 8 with 73% ee in 89% yield (Scheme 2). The use of bidentate chiral ligand 9b for the asymmetric conjugate addition afforded a 95:5 mixture of cis-adduct 8 with 91% ee in 92% yield. As a result, chiral ligand 9b was the best in terms of enantiocontrol for asymmetric conjugate addition. Importantly, the chiral ligand could be recycled and used without loss of enantiomeric excess. According to our retrosynthetic analysis, lactam 4 was synthesized in 6 steps from 8 (Scheme 3). We, however, found that 4 had low solubility that caused difficulty in further transformations. We therefore decided to oxidize the benzylic position at late stage of the synthesis. We turned to introduce the oxygen functionarities on the cyclohexane ring. Thus, 13 was converted into 19 in 20% yield over 10 steps (Scheme 5). The oxidation of 19 was accomplished under our condition9 to afford 20 in 80% yield. After deprotection, we achieved the asymmetric total synthesis of (+)-trans-dihydronarciclasine (2), whose specific rotaion, ^1H and ^<13>C NMR, MS, and IR data were consistent with those previously reported.

抄録全体を表示

Lundurine A, B, C, and D (1-4) were isolated from a Malaysian plant Kopsia tenuis by Kam and co-workers in 1995. They might be new seeds for anticancer drugs because selective anti-melanoma activities of Lundurine B and D have been reported. In addition, its unique hexacyclic skeleton including cyclopropane-fused indoline is attractive for synthetic organic chemists. Therefore, we have been studying total synthesis of Lundurines. According to Toke's protocol, iodine-mediated intramolecular cyclopropanation using 11 was studied (Table 1). Proper selection of solvent and temperature was important to prepare 10 with high yield and diastereoselectivity (entry 2, 6). 10 was converted into a cyclopropane-fused indoline 9 in 4 steps in good yield (Scheme 1). It is notable that 9 was unstable under acidic conditions, and removal of Boc group induced a cleavage of cyclopropane to give a quinoline 14 (Scheme 2). This tetracyclic lactone 9 was readily converted into a silyl enol ether 20 as a precursor of ring closing metathesis (Scheme 4, 5). Grubbs catalyst 2^<nd> generation was powerful enough for this cyclization to afford a tetracyclic cyclohexanone 6 after desilylation. To construct D and F heterocycles, introduction of nitrogen group on E ring was required (Scheme 6). Overman rearrangement seemed suitable for this purpose, because its intramolecular fashion might overcome some potential steric hindrance around E ring. Indeed, the rearrangement proceeded under heating condition to afford mixture of two diastereomers 26. Further investigations about construction of D and F rings are in progress. We recently started the second generation study on a synthesis of the tetracyclic structure of Lundurines using a new synthetic strategy: SmI_2-mediated reductive cyclopropanation (Figure 2). The key cyclization was proceeded well with addition of LiBr and afforded tetracyclic compound 27 (Scheme 7). This methodology enabled us to prepare 27 in shorter steps and higher yield.

抄録全体を表示

Naturally derived amino acids such as kainic acid (1), dysibetaine (2), and hydroxymethylglutamic acid (HMG, 3) are expected to serve as important leads for treatment of neuronal diseases. Here, we report our effort toward construction of their characteristic structure, a-monosubstituted and a,a-disubstituted α-amino acids, efficiently by short synthesis. We anticipated that, by using optically active amine for amine component as a chiral auxiliary, Ugi four-component coupling (U4CC) reaction would allow us to construct the amino acid framework in a stereoselective manner. As the optically active amine, (R)-2-amino-2-(4-methoxyphenyl)ethanol (4) was employed in the present study as shown in Scheme 1. The U4CC reaction of 4 with benzyl isocyanide, 2,2-dimethylpropionaldehyde, and octanoic acid provided 12 as a diastereomeric mixture, which was then converted into diastereomerically pure morpholinone 13 over three steps including acetylation, N-Boc formation, and alkaline methanolysis. Since methoxyphenyl and tert-butyl groups occupy pseudoequatorial orientation on the morpholinone ring, the methanolysis was apparently controlled thermodynamically. Finally, CAN-mediated ring opening followed by removal of the resultant 4-methoxyphenacyl group furnished (2S)-N-octanoyl-tert-leucine (15) in 14% overall yield for 6 steps. Furthermore, the efficiency was improved by shortening the number of steps to four, by employing convertible isocyanide 16 instead of benzyl isocyanide. Toward the synthesis of a,a-disubstituted a-amino acid, we first investigated efficient conditions for diastereoselective alkylation of morpholinone 18. After several experiments, we eventually found that potassium tert-butoxide and methyl iodide induce stereoselective methylation of 18 to give rise to 19 in 44% yield. Finally, we report asymmetric synthesis of IKM-159, a subtype-selective antagonist for AMPA receptor, by applying the U4CC reaction using optically active amine 4 as a chiral auxiliary. As shown in Scheme 5, the U4CC reaction using 2-furaldehyde and 3-iodoacrylic acid for aldehyde and carboxylic acid components, respectively, provided two diastereomeric oxanorbornenes 20 and 21. After acetylation, the diastereomers were separated, and the minor isomer was determined to be (2R)-isomer unambiguously by X-ray crystallography. By domino metathesis as a key reaction, the major isomer ((2S)-22) was led to heterotricycle 26. A series of functional group transformations then gave dimethyl ester 28. Through subsequent four steps for protecting group manipulations, we have successfully accomplished asymmetric synthesis of (2S)-IKM-159 (10). Total yield was 1.5% for 18 steps. (2R)-IKM-159 (11) was also synthesized by way of acetate (2R)-23 in 6.3% overall yield for 18 steps.

抄録全体を表示

Syringolin A (1), which was isolated from strains of the plant pathogen Pseudomonas synringae pv Syringae (Pss), possesses a 12-membered dipeptide ring structure containing two (E)-configured double bonds and a urea side chain. In 2008, syringolin A has been identified as a virulence factor which irreversibly inhibits the 20S proteasome. It was showed to selectively inhibit all three catalytic activities of eukaryotic proteasomes by covalent modification of a threonine residue in the active site. The proteasome is essential for protein degradation and has been validated in the clinic as a biological target for the treatment of multiple myeloma. Therefore, we are interested in syringolin A and decided to synthesize 1 and its analogues. Total synthesis of 1 has accomplished by Kaiser's, Stephenson's and Pirrung's groups. We planned to synthesize 1 and its analogues considering to develop more convergent synthetic route, which can be applicable to structure-activity relationship of 1. Our retro-synthetic analysis of 1 is depicted in Scheme 1. The substrate 3 with isonitrile and aldehyde functionalities was reacted with the carboxylic acid 4 and the amine 5 as the Ugi three component reaction. After optimization of Ugi reaction, the macrocycle 30 was obtained 26% yield. This synthesis allows us to construct the 12-membered dipeptide ring and introduce the urea side chain at once. Next, mesylation of the secondary alcohol, β-elimination and deprotection of the tert-butyl ester and the 2,4-dimethoxybenzyl group to afford syringolin A (1).

抄録全体を表示

Farnesyl diphosphate synthase (FPS) and geranylgeranyl diphosphate synthase (GGPS) are both classified into a trans-type prenyltransferase family, catalysing the fundamental chain elongation reaction between allylic diphosphate and isopentenyl diphosphate. The structural difference between FPS and GGPS has not been clarified. We have studied on the substrate specificities for FPS using various artificial substrate analogs and obtained much knowledge on the enzymic catalyst activity mechanism. However, there is little knowledge about the substrate recognition for GGPS. In this study, we examined reactivity of GGPS using the 3-alkyl IPP homologs. Moreover, we analyzed enzyme reaction from third dimensional viewpoint with docking simulation soft GOLD. Reaction of GPP with 3-alkylIPP using GGPS resulted in a condensation product with one molecules of IPP. However, the reaction with 3-butyl IPP produced nothing. It is considered that caused the steric hindrance of 3-alkyl group. Moreover, we speculated recognition mechanism of these allylic substrates of GGPS using molecular doking simulation soft GOLD.

抄録全体を表示

Aspergillus oryzae (Koji-mold) has been traditionally utilized for food productions in Japan, and is one of the model organism of filamentous fungi. In A. oryzae, only a few of secondary metabolites were identified except for some flavor compounds, while the genome sequence suggested that it possesses many genes responsible for biosynthesis of secondary metabolites. Recently, it was revealed that the unique chimera diterpene synthase was involved in fusicoccin biosynthesis in the fungi Phomopsis amygdali. Here, we show that a chimera diterpene synthase gene product in A. oryzae synthesizes a novel diterpene-type compound, kojidiene. A homologue of the chimera diterpene synthase was identified in the genomic database of A. oryzae. The ORF of this gene, named as A. oryzae diterpene synthase like I (AoDSL1), was cloned from cDNA libraly and heterologously expressed in Escherichia coll. AoDSL1 cyclized geranylgeranyl diphosphate (GGDP) to a diterpene hydrocarbon product but exhibited no catalytic activity as prenyltransferase. This was caused by the nonsense mutation in the prenyltransferase domain of AoDSL1. For NMR analysis of the cyclization product, a fully ^<13>C-labeled product was prepared from [U-^<13>C_6] mevalonate using the enzymatic synthesis strategy. The ^<13>C-NMR (inverse-gated ^1H-decoupling) and ^<13>C-^<13>3C COSY spectra of the compound proposed two substructures. Additionally, CT-HSQC and ^1H-^<13>C-^<13>C-^1H COSY was used to confirm the entire planar structure. Thus, NMR analysis revealed that AoDSL1 product represented a novel structure, given the name of kojidiene.

抄録全体を表示

β-Amyrin is widely distributed in plant kingdom. This triterpene is biosynthesized by the polycyclization reaction of (3S)-2,3-oxidosqualene that proceeds with regio- and stereospecific fashion. The substrate is folded in a chair-chair-chair-boat-boat conformation inside the catalytic reaction cavity. Many genes harboring β-amyrin synthase have been reported, but very little is known of the enzyme properties of pure β-amyrin synthase and the active sites for the catalysis. In this symposium, we report the successful isolation and the kinetic parameters of β-amyrin cyclase from Euphorbia tirucalli (monofunctional OSC) and the functional analyses of the active site residue (Phe728). The optimal catalytic conditions and kinetic parameters were as follows: 30℃, pH 7.0, 0.05% (w/v) Triton X-100, K_M: 27.6 μM, k_<cat>: 42.0 min^<-1> , k_<cat>/K_M: 1.52 μM^<-1> min^<-1>, specific activity: 352 nmol/min/mg. There are only two examples describing the kinetic data of OSC, i.e., human and bovine lanosterol synthases, but no report has appeared describing those of β-amyrin synthase and other OSCs. Based on the amino acid alignment, F728 is supposed to be an active site residue. Mutagenesis experiments of F into A, I and M resulted in significant loss of the enzyme activity, but the Tyr mutant had a high activity at the same level as the wild type, suggesting that Phe728 stabilizes the cation intermediates through cation/π interaction. From the mutant of F728H, various enzymic products were isolated that were generated mainly from dammarenyl, lupenyl and oleanyl cations. These results indicate that F728 residue is located at the D-E ring formation site and that this residue has a crucial role for stabilizing these cations through cation/π interaction. There is no report regarding the comparison of the enzymatic activities between OSCs and the mutants. The in vivo relative enzyme activities between the mutants and the wild-type were determined as follows. The expressed amounts of the proteins were estimated by a Western blotting method and the product amounts were determined by GC analyses. The product amounts were divided by the expressed protein amounts, which enabled to successfully determine the relative enzyme activities between each of the site-directed mutants.

抄録全体を表示

The putative biosynthetic pathways for paralytic shellfish toxins (PSTs) in cyanobacteria and dinoflagellates have been recently reported based on the corresponding gene clusters and genes required for saxitoxin synthesis found by Neilan and Jakobsen et al. We chemically synthesized some intermediates predicted in early stage in biosynthesis of PSTs, and attempted to identify them in the PSTs producing cyanobacteria, Anabaena circinalis, and dinoflagellates, Alexandrium tamarense, and also in a non-toxic strains of them using LC/MS. The arginine derivative bearing an ethyl ketone moiety, which was predicted as the first intermediate of PSTs biosynthesis, was detected in both of toxic strains of A. circinalis and A. tamarense. Analytical results for other intermediates will be also presented.

抄録全体を表示

The mushroom Stropharia rugosoannulata is called saketsubatake in Japanese, and wine-cap stropharia in English. It belongs to the family Strophariaceae, which is widespread in northern temperate zones throughout the world. It is edible and is cultivated for food. During screening for anti-Endoplasmic reticulum (ER)-stress and anti-Methicillin-resistant Staphylococcus aureus (MRSA) effects of the extracts of various mushrooms, we found activity in the extract of this mushroom. Recently we reported that several active steroids were isolated from this mushroom. In further search for bioactive compounds from the mushroom, we discovered four novel steroids with a very unique and completely unprecedented carbon skeleton. Fresh fruiting bodies of S. rugosoannulata were extracted with EtOH and then with acetone. After the solutions were combined and concentrated, they were partitioned between hexane and H_2O, CHCl_3 and H_2O, and then EtOAc and H_2O. The hexane-soluble part was fractionated by repeated chromatography. As a result, four novel compounds (strophasterols A to D) were purified. Their structures were determined by the interpretation of spectroscopic data. Strophasterols A showed anti-ER-stress and anti-MRSA activities.

抄録全体を表示

Chemical constituents of roots and evolutionarily neutral DNA base sequences of L. virgaurea collected in Hengduan Mountains and neighboring areas of China were studied. Fifty-one samples were classified into five chemotypes (types 1-5) on the basis of TLC analyses and isolated compounds. The major component(s) in each chemotype were virgaurenones A (1) and B (2) (type 1), ligularol (7) (type 2), cacalol (18) (type 3), 6-hydroxyeuryopsin (36) (type 4), and neoadenostylone (48) and its 1,10-epoxy derivative (50) (type 5), respectively. Fifty-nine terpenoids were identified, thirteen of which including seco-eremophilane derivatives (44 and 59) and sesquiterpene dimer (42) were new. The presence of genetic diversity was also suggested from the base sequences of evolutionarily neutral region in DNA. Two-types of base sequences in atpB-rbeL intergenic region were found, while three-types in ITSs region. These genetic types showed good correspondence to the chemotypes, although the latter one is a little more complex than the other. The collection sites of five chemotypes of L. virgaurea were overlapping, indicating that the environmental effects are not nearly concerned with the intra-specific diversity.

抄録全体を表示

Leishmaniaces are a group of tropical diseases caused by infections of a number of species of protozoan parasites belonging to the genus Leishmania that survive and multiply in macrophages in the mammalian host. The parasites are transmitted by female flying insects of the genus Phleobotomus and Lutzomyia. Leishmaniases currently affected 12 million people in developing countries annually. In many cases, medicines employed for treatment are toxic, only slightly effective, given by injection, or compromised by the development of resistance. Therefore, safe, effective, and affordable medicines for leishmaniases are needed in the developing country. We found that a Pakistani medicinal plant, Withania coagulans (Solanaceae), showed the activity. Thus, we tried to isolate leishmanicidal active compounds from methanol extract of aerial parts of W coagulans. An ethyl acetate (EtOAc) soluble fraction of the MeOH extract showed the strongest activity and a n-buthanol (n-BuOH) fraction showed weak activity. The EtOAc and n-BuOH fraction were purified by SiO_2 column chromatography and preparative HPLC using reversed phase column to give 22 new compounds along with over 25 known compounds. Almost of them were withanolide derivatives. Their structures were determined by HR-MS, 1D-NMR (^1H-NMR, ^<13>C-NMR), 2D-NMR and CD spectra. One of polyhydroxylated withanolides was determine its structure as (5R,6R,14R,15R,17S,20S,22R)-5,6,14,15,17,20-hexahydroxy-1-oxowitha-2,24-dienolide, and one of withanolide glycoside was determined its structure as (3R,14R,17S,20R,22R)-3,14,20-trihydroxy-1-oxowitha-5,24-dienolide 3-O-α-L-rhamnopyranosyl-(1→4)-β-D- glucopyranoside. These new and known withanolides were tested leishmanicidal activity against L. major, and some of these compounds showed the strong activity and had 1-oxo-2,5-dien partial structure.

抄録全体を表示

Scutellaria plants belong to the Lamiaceae family and include about 350 species. They are widely distributed in template zone and tropical zone of Europe, North America and East Asia and have been used as traditional medicines in many countries. For example, roots of them are used for removing fever and resolution in Chinese Traditional Medicines, while aerial parts of them are used as sedative and antispasmodic in United States. In previous study, flavonoids and diterpenes were mainly isolated from the Scutellaria plants, some of which showed biological activities such as anti-cancer, anti-inflammatory and anti-feedant activity and so on. As part of our investigation for searching new drug seeds, we have studied the chemical constituents of Scutellaria coleifolia. S. coleifolia were collected in Sichuan province, China, in August 2011. The air dried aerial parts of this plant (3.0 kg) were crushed and extracted three times with 70 % aqueous acetone for 72 hr at room temperature. The extract was successively partitioned with EtOAc, n-BuOH and H_2O. The EtOAc-soluble fraction (130.0 g) was separated by repeated column chromatography (silica gel, Sephadex LH-20, MCI gel CHP2OP, ODS MPLC, ODS HPLC) to give 14 new compounds (1-14), along with 4 known compounds (15-18). The structures of the isolated compounds were elucidated on the basis of extensive spectroscopic analyses. Compounds 1 and 2 were sesterterpenes with a γ-lactone moiety, structurally similar to manoalide derivatives. Our study provided the first examples of manoalide derivatives isolated from higher plants. Compounds 5-14 were neo-clerodane type diterpenes with a 13-spiro-15,16-γ-lactone structure, which are especially contained Scutellaria plants. The structure elucidation and biological activities of isolated compounds will be presented.

抄録全体を表示

The quantitative ^1H-NMR spectrometry (qHNMR) lead to absolute quantification of the organic compounds by comparing the signal integral of the particular compound with that of appropriate certified reference material. In this paper, we describe the application of this method to the quantitative determination of atractylon, which is unstable in air, in Atractylodis Rhizoma (dried rhizomes of Atractylodes ovata and A. japonica) and Atractylodis Lanceae Rhizoma (dried rhizomes of Atractylodes lancea and A.chinensis), and the content of atractylon in crude drugs was successfully determined. This method is also applicable for quantitative determination of chemical constituents in other crude drugs. Thus, the quantitative determination of amygdalin in Peach Semen (kernel of Prunus persica) and Armeniacae Semen (kernel of Prunus armeniaca), paeoniflorin in Paeonia Radix (dried root of Paeonia lactiflora), gentiopicroside in Gentianae Radix (dried root of Gentiana lutea), and columbin in Columbae Radix (dried root of Jateorhiza Columba) were also successfully carried out by qHNMR. The present method requires neither reference compounds for calibration curves nor sample pre-purification. It also allows simultaneous determination of multiple constituents in a crude extract. Thus, it is applicable to chemical evaluation of crude drugs as a powerful alternative of various chromatographic methods.

抄録全体を表示

Marine sponges belonging to the genus Halichondria are known to be a source of sesquiterpene isothiocyanates, isonitriles, and formamides and dimeric sesquiterpenoids with a urea linkage. During our search for structurally unique metabolites from Okinawan marine sponges, we have isolated five new dimeric sesquiterpenoids, halichonadins G-I (1-3), K (5), and L (6), together with one new sesquiterpenoid, halichonadin J (4), from the extract of an Okinawan marine sponge Halichondria sp. (NSS-2). The structures of 1-6 were elucidated on the basis of spectroscopic analysis and chemical conversion. Halichonadins K (5) and L (6) are structurally unique homo-dimers of the eudesmane sesquiterpene. The sesquiterepene moieties of them are connected to a piperidine ring through amide bonds, while 5 and 6 have a methyl acetate and a N-phenethylacetamide moieties, respectively, bonded to a nitrogen atom of the piperidine ring. The absolute stereochemistry of 5 was elucidated by a single X-ray diffraction analysis. Derivatization of 5 to 6 suggested that 6 have the same absolute stereochemistry as that of 5. Halichonadin K (5) showed moderate cytotoxicity against human epidermoid carcinoma KB cells (IC_<50> 10.6 μg/mL). Based on detailed analysis of the NMR spectra, halichonadins G (1) and H (2) were assigned to be homo-dimers of the eudesmane sesquiterpene linked through a methyl 2-{1-(2-amino-2-oxoethypureido} acetate fragment and a 2-hydroxymalonamide fragment, respectively. Halichonadin I (3) is a hetero-dimer of the eudesmane sesquiterpene with a urea fragment. The structure of halichonadin J (4) was disclosed to be a eudesmane type sesquiterpene possessing a 1-phenethyl urea moiety. Halichonadins G (1) and I (3) exhibited cytotoxicity against murine lymphoma L1210 cells (IC_<50> 5.9 and 6.9 μg/mL, respectively) and KB cells (IC_<50> 6.7 and 3.4 μg/mL, respectively).

抄録全体を表示

In the course of the investigation of biologically active substances from the rare plants, we isolated seven novel sesquiterpenoids, named euonymusins A〜G (1〜7) from the fruilts of the rare plant Euonymus chibae. Their absolute stereostructures were established by a combination of Mass, IR, 2D-NMR and CD spectra, and chemical reactions such as alkaline hydrolysis. The cytotoxic activities of compounds 1〜7 against three cancer cell lines (RERF-LC-KJ: lung cancer; HeLa:cervical cancer; and HSC-2:oral cancer) were examined. Compounds 5 and 6 selectively showed the strong cytotoxic activities against RERF-LC-KJ. A large amount of pigment (8) was isolated from the leaves of E. chibae. Compound 8 was identified as methyl phaeophoride a by FAB-Mass, IR, UV, and NMR spectra. It was possible to assign all carbon signals of compound 8 by measurement of 2D-INADEQUATE in pyridine-d_5.

抄録全体を表示

Shikimic acid was first isolated in 1885 by Eijkman from the fruit of the Japanese plant Illicium religiosum. Many natural plants contain shikimic acid for biosynthesis as an important intermediate. Roche pharmaceutical uses shikimic acid from star anise as a starting material for production of Tamiflu. However, isolation of star anise from natural resources has been limited. Here we report efficient and new isolation protocol of shikimic acid from Ginkgo biloba leaves utilizing an ionic liquid that dissolves cellulose. Shikimic acid was efficiently extracted and isolated from G. biloba leaves utilizing an ionic liquid 1-butyl-3-methylimidazolium chloride ([bmim]Cl), which is able to dissolve cellulose. Using the ionic liquid at 150 ℃ gave an extraction yield of 2.3% w/w for shikimic acid, which was 2.5 times higher than that for methanol at 80 ℃ (0.93% w/w). Meanwhile, an isolation protocol for obtaining shikimic acid in good yield from the IL phase using an anion-exchange resin Amberlite IRA-400 Cl form was established. The SEM micrograph of the leaves after extraction showed a significantly different morphology, with the larger features completely broken down into much smaller structures, indicating that the G. biloba leaves were much more highly dissolved in [bmim]Cl compared to in methanol The present procedure could lead to a convenient supply of shikimic acid, thus enabling production of greater amounts of the antiviral agent Tamiflu. The protocols are also likely to be applicable to other plant leaves, allowing for isolation of greater quantities of other natural products as well as unknown natural compounds.

抄録全体を表示

Propolis is a natural substance that honeybees, Apis inellifera, collect from buds and exudates of certain trees and plants. It has various biological activities such as antibacterial, anti-inflammatory, antioxidant and anticancer properties, and has long been used as a folk medicine in many regions of the world. The chemical components of propolis depend on the vegetation at the region of collection, since honeybees preferentially target plants grown near beehives as sources of propolis. Previously, we found that the components of propolis from Jeju Island, Korea, located off the southern coast of Korea, differ from propolis from other regions. To investigate the potential utility of propolis, we further studied the components of propolis from Jeju Island. Eight new chalcones and nineteen known compounds were isolated, and the structures of these compounds were determined by spectroscopic analyses. Moreover, we identified the plant origin of propolis from Jeju Island as Angelica keiskei by the observation of honeybee behavior and phytochemical analysis. Ethanol extracts of the propolis from Jeju Island (EEPJ) had the promotion effect on NGF (nerve growth factor) secretion in human glioblastoma T98G cells. The promotion effect of EEPJ was a characteristic biological activity not presented in other propolis such as Brazilian (Baccharis type) and Uruguayan (Populus type) propolis.

抄録全体を表示

We have isolated several hundreds of resveratrol oligomers (RO) from the families of Dipterocarpaceae and developed the fundamental database useful for both elucidating structures and identifying bioactivities. Some isolates ranging from dimer to tetramer that contain resveratrol blocking units have attracted synthetic chemists and been regarded as challenging targets for high regioselective strategy. Therefore an approach for expansion of chemical library of RO will not only contribute to discovery of new lead compounds, but also provide valuable information for synthetic and medicinal chemists. In the current study, we focused on the highly polar components present in Upuna borneensis and proceeded comprehensive investigation of the acetone extract, which resulted in the isolation of a new resveratrol octamer, upunaphenol Q (1) together with 23 phenolic compounds (2-24). The relative structure of 1 was elucidated by usual spectroscopic methods, including 1D- and 2D-NMR experiments at -10℃ and high-resolution electron spray ionization mass spectral analysis. With the help of our chemical library, the obtained isolates enabled the skeleton-based comparative study of CD spectra for the determination of absolute configuration of stilbene scaffolds. This is the first report to determine the absolute configuration of highly condensed stilbenoids, demonstrating that the ring systems of RO possess the peculiar CD properties in common. Using dehydroxylated derivatives, we further compared the experimental and calculated CD spectra. It was found that this dehydroxylation method can dramatically reduce the number of dominant conformations and make CD calculation applicable for the determination of absolute configurations of RO.

抄録全体を表示

Filamentous fungi are well-known producers of a large number of diverse natural products, many of which have fascinating structures and important biological activities that have attracted the attention of natural product chemists, organic chemists, and pharmacologists. As fungal genomes have been sequenced, it has become clear that there are far more secondary metabolite-encoding biosynthetic gene clusters than were evident in previous chemical studies. This suggests that fungi have dozens of unique gene cluster coding for uncharacterized polyketides and nonribosomal peptides. Many of these gene clusters are said to be transcriptionally suppressed under standard laboratory culture conditions. Recently, it was demonstrated that epigenetic modification compounds, such as histone deacetylase (HDAC) inhibitors or DNA methyltransferase inhibitors, could induce transcriptional up-regulation of many PKS and NRPS-encoding gene clusters in a model fungus, Aspergillus niger. In an effort to obtain novel bioactive polyketides, we applied these chemicals to cultures of Chaetomium species. Cultivation in the presence of suberoyl bis-hydroxamic acid (SBHA) (Zn^<2+> type HDAC inhibitor), followed by extraction, resulted in the isolation of novel prenylated polyketides 1-11 from Chaetomium indicum. Among the compounds, 9-11 possessed unprecedented polycyclic polyketide frameworks possibly generated via a [4+2] cycloaddition. On the other hands, addition of nicotinamide (a NAD^+ dependent HDAC inhibitor) to the culture medium of C. mollipilium significantly enhanced a series of C_<13>-polyketides production and led to the isolation of five novel C_<13>-polyketides (12-16) along with (-)-aureonitol and spiroketal 17. The structures of 1-17 with absolute stereochemistries were elucidated by spectroscopic analysis, vibrational circular dichroism (VCD), X-ray single crystal diffraction studies, and chemical trans formations and we describe plausible biosynthetic pathways to account for their biosynthetic relationship. This study suggested that both types of HDAC inhibitors are useful to obtain diverse fungal polyketides via activation of silent biosynthetic pathways.

抄録全体を表示

Aphids produce novel pigments, such as the protoaphins, furanaphin, and the uroleuconaphines, which may possess interesting biological activities such as cytotoxicity. The presence of pigments is also important for expressing aphid body color, and it is presumed that subtle differences body coloration (color polymorphism) affect predator-prey interactions. Therefore, the unique structures and potentially important biological activities of aphid pigments are of interest. A green pigment, viridaphin A_1, glucoside (6), was isolated from the green aphid Megoura crassicauda. One- and two-dimensional NMR spectrometric analyses of 6 and its aglycone established the structure as an octacyclic compound. Viridaphin A_1 glucoside exhibited cytotoxicity against HL-60 human tumor cells with an IC_<50> of 23 μM. Four red pigments isolated from Uroleucon nigrotuberculatum were evaluated for their growth inhibition activity against insect pathogen, and it was found that 2 exhibited the activity against Deuteromycotina Lecanicillium sp, and 2, 3 and uroleuconaphin A_1 glucoside (12) exhibited the activity against Entomophthorales Conidiobolus obscurus. On the basis of these biological activities, we hypothesize that aphid pigments may protect aphids from invasive species, such as viruses, bacteria, and fungi.

抄録全体を表示

Hypoxia-inducible factor (HIF) is a transcriptional factor that is deeply involved in cancer progression; HIF promotes angiogenesis and glucose/energy metabolism for cell survival in the low-oxygen environment. Among several HIF subunits, the O_2-regulated HIF-lα and HIF-2α are promising target molecules for cancer chemotherapy. During the course of our screen for novel HIF-signaling modulators from natural sources, we re-discovered verucopeptin (1) as a new HIF-signaling inhibitor. 1 was originally isolated as an antitumor compound from the culture broth of Actinomadura verrucosospore (J. Antibiot. 1993, 46, 921). In spite of the potent biological activity, however, the absolute stereochemistry still remains unknown. Herein, we report the determination of the absolute stereochemistry of 1. Verucopeptin (1) is composed of a cyclic depsipeptide unit and a polyketide side chain. The cyclic depsipeptide consists of six amino acid residues: one residue each of piperazic acid and β-hydroxy leucine, and four glycine residues. The polyketide side chain exists in a dynamic equilibrium between a cyclic acetal form and a linear keto form in solution, making the stereochemistry assignment difficult. We first determined the absolute stereochemistry of amino acid residues by advanced Marfey's method. Hydrogenolysis of 1 followed by acid hydrolysis furnished a mixture of amino acids, which was condensed with L-FDAA. We compared the retention times of the L-FDAA derivatives on LC-MS with those of the authentic samples, revealing the presence of D-piperazic acid and L-erythro-β-hydroxy leucine. To determine the six stereogenic centers in the keto-form side chain, we carried out a series of derivatization reactions and synthesis of authentic samples. First, we prepared a reduced derivative 2 by NaBH_4 treatment. The emerging 1,2-diol function was protected as an isopropylidene derivative to reveal the 23S^*, 24S^* stereochemistry by NMR analysis. The relative stereochemistry of C27 and C28 was deduced by NMR analysis of 1 in the acetal form to be S^* and R^*, respectively. In combination of these results with that of the modified Mosher's method applying to C24 and C28, the absolute stereochemistry around the THP ring was determined to be 23S, 27S and 28R. Next, we challenged determination of the absolute stereochemistry of the 1,3,5-trimethyl alkyl chain. 1 was treated with RuCl_3 in the presence of NaIO_4 to obtain 2,4,6-trimethyl octanoic acid 5. The carboxylic acid 5 was subjected to the PGME method to reveal the 31S stereochemistry. The stereochemistry of C33 and C35 was determined by comparing the ^1H NMR spectra of the natural carboxylic acid with those of the four diastereomers of 5, synthesized by tandem diastereoselective alkylation. Spectroscopic analysis revealed the 33S and 35R stereochemistry. In summary, we determined the stereochemistry of 1 as 10R, 15S, 16S, 23S, 27S, 28R, 31S, 33S, 35R. 1 potently inhibited the HIF-signaling pathway with an unknown mechanism. The information of the stereochemistry will be of great help to deduce the pharmacophore of 1. Detailed analysis of the mode of action and SAR are in progress.

抄録全体を表示

By the newly developed assay method, a novel glycolipid Acremomannolipin A (1), isolated from the fungi Acrernonium strictum, was identified as a potent calcium signal modulator. The structure of 1 elucidated on the basis of intensive spectroscopic analyses as well as its degradative studies was quite unique, the D-mannopyranose being connected with D-mannitol through a β-glycoside linkage. All the hydroxyls in the mannose were highly masked as peresters with aliphatic acids, and the moiety being made hydrophobic, whereas the mannitol part exerting the highly hydrophilic property. The first total synthesis of acremomannolipin A (1) was also achieved in this study by employing the characteristic stereoselective β-mannosylation of 4,6-O-benzylidene-protected mannosyl sulfoxide with a D-mannitol derivative in the presence of trifluoromethanesulfonic anhydride as the key reaction. The physical and spectroscopic properties were completely in accord with those of the natural Acremomannolipin A. [chemical formula]

抄録全体を表示

Neurotrophins are recognized as important regulatory substances in nervous system. However, they cannot pass across brain-blood barrier because of the properties of their high molecular weight. To address this issue, considerable efforts have been made to find small molecules that mimic neurotrophic properties. As part of our efforts to discover natural products with neurotrophic properties, we investigated the Me0H extract of the root of BANGLE (Zingiber purpurenum) that exhibited neuritogenesis activity in PC12 cells at 25 μg/mL, resulting in the isolation of neurotrophic compounds 1 and 2, and 3 as a new compound. In this symposium, we present the structure elucidation of 3 and neurotrophic effects of 1 and 2 on cultured cells as well as on OBX mice. The Me0H extract of BANGLE was fractioned by bioassay-guided fractionation using PC12 cells to give 25 chemical components. The structure of new compound 3 was elucidated by analysis of spectroscopic data and comparing the NMR data with cussumunarin A (4), and its absolute configuration was determined by CD spectrum. Compounds 1 and 2 found not only to significantly induce neurite sprouting of PC12 cells, but also to increase the neurite length and number of neurites in primary cultured rat cortical neurons, and also showed protective activity against cell death caused by deprivation of serum. Furthermore, chronic treatment of these compounds enhanced hippocampal neurogenesis in dementia model OBX mice. These results suggested that compounds 1 and 2 have both neurotrophic effects and neurogenesis, and thus BANGLE may be developed as a valuable food additive for potentially protecting neurodegenerative disease.

抄録全体を表示