A novel construction method for the steroid skeleton such as 6,(5β)-Androstene-3,17-dione (1) by the transannular Diels-Alder reaction of macrocycles and a discussion of the diastereo-selectivity of this reaction based on MM2 transition structure models are presented. In this synthesis, transannular Diels-Alder reaction of the 14-membered diketone 3, prepared by the intramolecular alkylation of the protected cyanohydrin 14, provide all the relative stereo-chemistries among the A, B and C-rings. The trans stereochemistry between C(13)-methyl and C(14)-hydrogen in 3 is introduced by the Michael addition of the vinyl cuprate 6 to the enone 5 and subsequent β-methylation of the resulting enolate.
Total synthesis of (±)-11-oxoprogesterone(4), (±)-adrenosterone(5) and (±)-estrone(38) has been accomplished, and a synthesis of the (+)-trans-hydrindan(46) which is a potential intermediate for the synthesis of (+)-aldosterone(1) has been developed as an optically pure form using intramolecular Diels-Alder reaction as a key step. Total Synthesis of (±)-11-Oxoprogesterone(4) Thermolysis of the olefinic benzocyclobutene(10) afforded the trans-hydrindan(11) stereoselectively. The compound(11) was transformed into 11-oxoprogesterone(4), which is a known precursor of corticosteroids, via 19-nor-Δ^9-progesterone(18) and Δ^9-progesterone-(22). Total Synthesis of (±)-Adrenosterone(5) and (±)-Estrone(38) A conspicuously high diastereoselective synthesis of the trans-hydrindan(33) was achieved by the thermolysis of the ketal(28). The compound(33) was converted into the dienedione(37), which had been transformed into estrone(38) by S. Danishefsky. Also the trans-hydrindan(33) was transformed into (±)-adrenosterone(5) via the enedione(42) by a several-step sequence. Synthetic Approach to (+)-Aldosterone(1) A highly stereoselective synthesis of the (+)-trans-hydrindan(46) as an optically pure form has been accomplished by the thermolysis of the thioacetal(45c).
The organoselenium-mediated reduction of α,β-epoxy ketones to β-hydroxy ketones has been reported as a new and promissing entry to a variety of acyclic and cyclic aldols. A variety of acyclic and cyclic epoxy ketones smoothly reacted with 3 equiv of PhSeNa in ethanol in the presence of 0.5 equiv of AcOH to give the corresponding β-hydroxy ketones (aldols) in excellent yields. Reaction conditions are neutral and formation of enones (dehydration products) were, if any, less than several percent. In particular, non-formation of enones was observed in the case of acyclic epoxy ketones. This method has been demonstrated to be effective in complex molecules having polyfunctional groups by the successful synthesis of some santanolides such as (+)-dehydro-isoerivanin (3), (+)-isoerivanin (4), (+)-ludovicin C (5), and (+)-1α, 3α-dihydroxyarbusclin B (6). The highly stereoselective total synthesis of (-)-picrotoxinin (10), the most toxic compound of plant origin, was also achieved by the use of this methodology as a key step. The contiguous eight asymmetric centers incorporated in picrotoxinin have been constructed under virtually complete stereoselectivity.
Reaction of 3-sulfolenes with various electrophiles in combination with stereoselective desulfonylation provided a new method for synthesizing (E)-, (E,Z)-, and (E,E)-conjugated dienes with exceedingly high stereoselectivity. 3-Sulfolenes (1) react with primary alkyl iodides, aldehydes, ketones, and α,β-unsaturated ketones to give the corresponding α-substituted 3-sulfolenes. The substituents on the 3-sulfolene ring exhibit remarkable effect on the regioselectivity of the reaction with electrophiles. Electron donating groups on the double bond effect selective substitution at the 2-position, while electron withdrawing groups cause substitution at the 5-position. When one of the α-position of the sulfolene is occupied by an alkyl group, electrophiles are exclusively introduced to the other α-position. A new method is developed for desulfonylating trans-2,5-substituted 3-sulfolenes (4) exclusively to (E,E)-conjugated dienes (10). The method is applied to the highly stereoselective syntheses of three insect pheromones having conjugated diene structure and monoterpene (E)-tagetone (17). Convenient methods for synthesizing hydrindane derivatives are developed by utilizing the diene synthesis in combination with intramolecular Diels-Alder reaction. The method is applied to the completely stereoselective synthesis of coronafacic acid (22), and asymmetric synthesis of the CD-ring and C(20)-C(22) part of vitamin D (26).
Synthesis of (±)-ptaquilosin (2), the aglycon of ptaquiloside (1) a carcinogenic substance of bracken fern is described. δ-valerolactone (3) was converted by seven-step sequence into a bromo ketone (5c), the intramolecular alkylation of which afforded a cis-hydrindane compound (6). A cyclopropyl unit was constructed in the compound (6) to give a ketone (7a). The hydroxy group was introduced into a cyclopentane moiety of ketone (7a) by following sequence: 7a→12→13→14. Highly stereoselective addition of a Grignard reagent to the ketone (14) followed by Swern oxidation of the resulting diol (15a) afforded a ketone (16), which was methylated by the Kuwajima's method to provide a compound (17a). The compound (17a) was converted into an aldehyde (20). Introduction of a hydroxy group at the ring juncture was effected by autoxidation of the aldehyde (20) and subsequent reduction of the resulting hydroperoxide (21) to give a desired alcohol (22). Finally, the alcohol (22) was converted by two-step sequence into ptaquilosin (2) (1.1% overall yield from δ-valerolactone).
Total syntheses of the levorotatory enantiomer of punctatin A (antibiotic M95464) and the dextrorotatory enantiomer of punctatin D (antibiotic M167906) have been achieved. The identities of the synthetic materials with the corresponding natural products, which were confirmed spectroscopically and by [α]_D, permitted the assignment of absolute configuration. These structurally novel trans fused tertiary alcohol antibiotics were constructed in 16-19 steps from optically pure (99.6% ee) dextrorotatory diketone 5. Central to the synthetic strategy was (i) utilization of the Still rearrangement as a viable means for elaborating an angular hydroxymethylated cis-perhydroindan system and (ii) construction of the completely functionalized four-membered ring in proper stereochemical disposition by application of Norrish type II photochemistry. The conformational bias shown by selected intermediates and certain of their stereoisomers will be also discussed.
Manoalide isolated from the sponge is a nonsteroidal anti-inflammatory agent. This sesterterpenoid also showes not only significant activity against Gram positive bacteria but also inactivate directly phospholipase A_2 which is a rate limiting enzyme in phospholipid metabolisms and prostaglandin synthesis. Beside manoalide, seco-manoalide, E- and Z-neomanoalide were isolated from the same sponge. We report here the first and highly efficient syntheses of manoalide, seco-manoalide, and E-neomanoalide. For the synthesis of manoalide, the construction of γ-hydroxybutenolide moiety is the main problem. As the efficient synthetic method of γ-hydroxybutenolide possessing various substituents had not been established yet, we have developed the general synthetic method by photosensityzed oxygenation of substituted α-trimethylsilylfuran, and chemo-selective oxidation of furan ring has been achieved (Table 1). 3-Substituted-5-trimethylsilylfuran derivative 11 required for the synthesis of manoalide was obtained by two methods. One is the connection of allylchloride 4 with α-alkoxystannane 10, and the other is the Pd(0) catalized coupling of 4 with CO and stannylfuran 15. The synthesis of manoalide and seco-manoalide was achieved from compound 11 by the sequences shown in scheme 4 and 6. E-neomanoalide was also synthesized by the similar method which was shown in scheme 7. These synthestic study may help for understanding the action mechanism of phospholipase A_2.
Preparation of chiral building blocks by biochemical methods including asymmetric reduction with baker's yeast, utilization of biopolymer and asymmetric hydrolysis with lipase is described. The following topics are discussed. 1) Both the enantiomers of ethyl 3-hydroxybutanoate [1a] were prepared and utilized as the chiral starting material for the synthesis of pityol . 2) A hydroxy ester  was prepared by baker's yeast reduction of oxoester  and utilized as the chiral starting material for the synthesis of sporogen AO-1 . 3) Asymmetric reductions of symmetrical diketones [9,14] by yeasts were carried out, and the products [8,13] were converted to JH III , JH I , and JH II . 4) Bridged symmetrical diketones [23,26] were reduced by baker's yeast to give hydroxy ketones [22,24]. The latter is a chiral starting material for the synthesis of glycinoeclepin A . 5) A monoacetate (+)-[27a], useful starting material for the synthesis of optically active prostaglandins, was prepared using hydrolysis of readily obtainable substrate by commecially available lipases.
Chiral cyclopentane derivatives have widely been employed as important starting materials in the syntheses of naturally occurring compounds. Development of an efficient preparation of a chiral cyclopentane derivative from readly available substances with both (+)- and (-)-forms is therefore desirable. We have established an efficient procedure for the preparation of chiral 2-isopropeny1-5-methyl-4-oxocyclo-pentane-1-carboxylate(1) and (2), whose substituents would be transformed into variety of functional groups, from readily avairable (-)- and (+)-carvone. First, the (-)-isomer(1) was employed in the synthesis of (+)-tecomanine (7), an antipodal form of hypoglycemic monoterpene alkaloid, where the aminylium ion-induced cyclization played an important role. Whereas, N-acetyl-L-acosamine (32), found as a structural component of glycosidic antibiotic, was also derived from the (+)-isomer (2) by utilizing the Beckmann rearrangement and Baeyer-Villiger oxidation as key reactions. Finally, Melillo's lactone(34), a key intermediate for the synthesis of carbapenem antibiotic (+)-thienamycin, was prepared from (-)-isomer(1) by manipulation of its substituents in reasonably high-yield.
We have developed a general strategy for obtaining a variety of chiral building blocks from the common chiral synthon 2 and exploitation of these building blocks to the synthesis of various nitrogenous natural products having biological activities. 4-O-Benzyl-2,3-O-bis(methoxymetyl)-L-threose (2) as a chiral synthon, readily available from diethyl L-tartrate in 45% overall yield, was subjected to 1,2-asymmetric induction based on nucleophilic addition of organometallic or metal hydride reagents to both aldehyde and ketones for constructing new asymmetric centers. These addition reactions could diastereofacially be controlled by selections of nucleophiles and the protective group of the substrate and proceed either via α-chelation or Felkin models, affording anti-Cram or Cram isomers, respectively. The building blocks with D-xylo and D-lyxo frameworks, thus prepared, were converted to (-)-N-benzoyl-L-daunosamine (19b) and (-)-anisomycin (26), respectively, both in enantiomerically pure forms. Similarly, L-ido, D-gluco, L-gulo, and D-manno building blocks were transformed to (+)-codonopsinine (14) and its stereoisomers 17, 3, and 18, respectively. Furthermore, in hydride addition to the ketones, employment of Zn(BH_4)_2 and L-Selectride (or LS-Selectride) as reducing agents proved to lead to highly diastereoselective formation of corresponding anti-Cram alcohols (92->98% d.e.) and Cram alcohols (84-96% d.e.), respectively. These results were efficiently applied to the first total synthesis of (+)-monomorine I (35) in natural form and its diastereoisomeric alkaloids (-)-gephyrotoxin 195B (36) in enantiomeric form of the natural products.
Two potentially useful enantioselective routes to the kainoid amino acids have been developed based on two intramolecular pericyclic reactions using diethyl (L)-tartrate and (S)-O-benzylglycidol as chiral starting materials, respectively. Reaction of the δ,ε-unsaturated aldehyde 29c, prepared from diethyl (L)-tartrate, with Meldrum's acid 7 afforded a single adduct 31b diastereoselectively via spontaneous condensation and intramolecular hetero-Diels-Alder reaction. Hydrolysis of 31b gave the bicyclic lactone 32b bearing newly generated three contiguous chiral centers on the pyrrolidine ring whose structure was confirmed by converting it into kainic acid lactone 33, the known compound generated from kainic acid 1 by acid treatment. Reduction of 32b, followed by regioselective dehydration of the product 34 yielded the potential intermediate 35 of kainic acid 1. On the other hand, thermolysis of both alkyl-44a and aryl-44b-cis-olefinic aziridine esters, 44a and 44b, prepared from (S)-O-benzylglycidol 40, yielded the corresponding all-cis-trisubstituted pyrrolidines, 45a and 45b, diastereoselectively, via spontaneous generation of the 1,3-dipoles, 43a and 43b, and their intra-molecular [1,3]-dipolar cyclization. The former adduct 45a was converted into the potential intermediate 50 of kainic acid 1 via the α,β-unsaturated aldehyde 48. The latter adduct 45b was successfully transformed into acromelic acid A 4, toxic principle of the poisonous mushroom Clitocybe acromelalga, via highly stereoselective epimerization of the all-cis-diester 54.
(-)-Bulgecinine (2) and carbapenems (3) have been synthesized from L-pyroglutamate (1) using as a bifunctional chiron without a prior modification. In the synthesis of (-)-bulgecinine (2), the regioselective enolate of L-pyroglutamate (1) was treated with 2-toluenesulfonyl-3-phenyloxaziridine to furnish (4R)-alcohol (4a). Hydroxylation was highly selective (>98% d.e.) and no racemization was detected. (-)-Bulgecinine (2) was synthesized from the alcohol 4a in 7 steps. The combination of regioselective addition reaction of a ester enolate to the lactam (1) and chirospecific pyrrolidine ring formation of the ester (12) was the main strategy in the synthesis of carbapenems. Various ester enolates gave the mono adduct (12) which on hydrogenolysis followed by hydrogenation at medium pressure gave 2,5-cis pyrrolidine derivative (14) exclusively. The pyrrolidine (14) were converted to carbapenams (15) and then to carbapenems (3).
Recently, we reported the first successful chiral alkylation onto 4-acetoxy-2-azetidinones (3 and 6 employing the tin(II) enolates of C4-chiral-3-acyl-1,3-thiazolidine-2-thiones (1a-d and 12) and its application to the chiral synthesis of 1β-substituted carbapenems (11 and 15). Now, we expanded this chiral tactics to alkaloid syntheses. Chiral alkylation of 5-acetoxy-2-pyrrolidinone (18) or 6-acetoxy-2-piperidone (21) with the tin(II) enolates of 3(ω-chloroalkanoyl)-4(S)-isopropyl-1,3-thia-zolidine-2-thiones(22a-d) furnished the corresponding alkylated products 24a-d in a highly diastereoselective manner (≧93 - ≧97%de) and in 57-73% yields. Subsequent reductive annulation of 24a-d with LiAlH4 at 0℃ and then under reflux gave directly the desired bicyclic products 33a-d in 41-69% yields together with the corresponding hydrogenolysis by-products 34a-d. Compounds 33a (≧99%op) and 33d proved to be (-)-trachelanthamidine and (-)-epilupinine, respectively. Naturally occurring (+)-epilupinine (37)(≧97%op) was similarly synthesized. A unified mechanism 30 for the stereochemical outcome of the chiral alkylation and new empirical aspects (Figure 1) for the reductive annulation toward the N-atom-containing bicyclic compounds are also discussed in the text. Thus, we succeeded in developing an extremely short chiral synthesis of the bicyclic alkaloids involving pyrrolizidine, indolizidine, and quinolizidine skeletons.
The first total synthesis of RA-VII and deoxybouvardin(RA-V) is described. The synthetic strategies are shown in Chart II. Among them, Route A was only successful. It comprises construction of the 14-membered ring unit 3 and subsequent coupling with tetrapeptide 4. For the construction of the 14-membered ring, which is crucial to this strategy and should be versatile intermediate leading to related compounds, we employed two methods, Route A-1 and A-2. A-1 is intramolecular amidation of linear diphenyl ether 13 (Scheme I). A-2 is intramolecular oxidative coupling of two phenolic parts of dipeptide by thallium trinitrate (Table I, II). A-1 did not give 14-membered ring but dimeric 28-membered one. A-2 afforded 14-membered rings. Thus the oxidation of dichloro dibromo derivatives 20 gave the desired 14-membered ring 23. But tetrabromide 17 was found to cyclize in the opposite fashion comparing with RA. Conversion of 23 to RA-VII was achieved by the successive treatment illustrated in Scheme III and IV. Selective demethylation of RA-VII with AlCl_3 gave deoxybouvardin (RA-V). Other strategies, via 18- and 26-membered ring (Route B and C) are also reported (Chart I).
Rhizoxin is a novel 16 membered macrolide, isolated from Rhizopus chinensis Rh-2 which causes rice seedling bright, posesses a unique structure having a chromophore-side-chain, and exhibits potent antifungal and remarkable antitumor activity. Under considering the structure-activity relationships, we have studied toward the total synthesis of Rhizoxin. Our convergent synthetic plan derived from a retrosynthetic analysis, was designed to assemble three building blocks, chromophore-side-chain, right-wing, and left-wing. Thus, chromophore-side-chain was synthesized from 2-methyl-5-ethoxycarbonyloxazole as a starting material, and the right-wing was synthesised starting from a novel chiral half ester (Ethyl hydrogen (3S)-3-[3-Phenyl-(E)-2-propenyl] glutarate), which was created by using asymmetric hydrolysis of the corresponding prochiral di-ester with PLE. The half ester was converted into right-wing via several steps using a cyclic hydroboration as a key reaction. The Left-Wing offers challenging problems to construct such partial structures as A(syn-form) and B(anti-form). A new methodology to construct such moieties has been developed and the synthetic study on the left-wing using the methodology will be mentioned.
Here will be described the enantioselective synthesis of oleandolides (7 and 9) from the polyketide lactone 8 derived from oleandomycin (1) as a chemical simulation of path B. The aglycone 7 was obtained in 75% yield from 5 in 3 steps through removal of the amino sugar moiety by treatment of the N-oxide with trimethylsilyl iodide. Exhaustive oxidation of the four hydroxyl groups in 7 was realized by exposure to RuO_4 in CCl_4 to give the polyketide lactone 8 (M^+ 366). The reduction of 8 was achieved by Zn(BH_4)_2 in the presence of MgBr_2 to provide stereo-selectively the tetraol 9 as cubes in 80% yield. The absolute structure of the macrolide was defined by the X-ray crystallographic analysis to be (5R, 8R, 9R)-9-dihydro-8-methyl-epi-oleandolide (9) as depicted in Fig. 1. The stereochemistry of the macrolide 9 was incompatible with that of the natural macrolide 2 only at the C-5. The reduction of 8, however, without MgBr_2 gave a 1: 1 mixture of 7 and 9. On the other hand, the C-9 ketone 14, which was obtained from 7 by selective benzylidenation and oxidation, was led to the biosynthetic precursor 2 by catalytic hydrogenation.
The unique structure of erythromycin A has attracted the attention of many chemists and syntheses of erythronolide A, an aglycone of erythromycin A, and erythromycin A itself have been achieved already by more than five groups in recent years. In most of these synthses, the stereocontrol on the cyclic system has been adopted for the introduction of chiral centers in these acyclic systems. In our case, the synthesis of this antibiotic was challenged based on acyclic stereoselection. 2,3-syn-2-Methyl-3-hydroxyesters 1a,b were synthesized from optically active imide 9 in several steps including a stereoselective reduction of β-ketoimide 8 by Zn(BH_4)_2, and were converted into segments 4 (left half) and 18 (a part of right half), respectively. (Me_2PhSi)_2NLi promoted condensation of these segments gave a desired C8-α-methyl compound 19a. However, all attempts for removal of the unnecessary hydroxy group at C_7 was unsuccessful. Thus, hydrogenation of the enone 20, obtained by mesylation of C_7-OH group followed by base treatment was examined, and the desired C_8-α-methyl-ketone 21 was obtained with unexpectedly high stereoselectivity. The compound 21 was successfully converted into the aldehyde 23b. Since erythromycin A has been derived from 23b by Woodward et al., the present work constitutes a formal total synthesis of erythromycin A. Aldehyde 5 corresponding to a right half segment (C_1-C_7) was also synthesized. Starting from 4a and 5, synthesis of the seco-acid derivative 28 involving all chiral centers necessary for erythronolide A synthesis is now in progress.
The first total synthesis of (+)-nogarene (4) and (+)-7-deoxynogarol (3), representative nogalamycin congeners, have been accomplished. Nogalamycin (1) and its related compounds are notable anthracycline antibiotics because of their unique structures and prominent antitumor activities. Chiral Synthesis of the DEF-Ring System: Exploration of a new synthetic scheme to construct their characteristic DEF-ring system in an optically active form was first examined. Thus, the methylketone (7) was synthesized from (+)-benzyl D-gentosaminide (5) obtainable from D-arabinose. Addition of 1-lithio-2,5-dibenzyloxy-3,4-dimethylbenzene to 7 took place stereoselectively to afford the alcohol (9). This was elaborated to the hydroquinone (11). Brief exposure of 11 to TMSBr effected intramolecular acetal formation. Acetylation of the resulting acetal furnished the DEF-ring system (12). Chiral Synthesis of the CDEF-Ring System: The alcohol (21) obtained by stereoselective addition of 2-lithio-1,4,5,8-tetramethoxynaphthalene to 7, was converted into the naphthalene (22). Oxidation of 22 with CAN was found to occur regioselectively to yield the 1,4-naphthoquinone (23) as a major product. After reduction of 23, intramolecular acetal formation of the 1,4-dihydroxynaphthalene (25) gave the diacetate (26). This was derived to the CDEF-ring system (27) by cleavage of the methyl ethers and oxidation. Total Synthesis of (+)-Nogarene and (+)-7-Deoxynogarol: Diels-Alder reaction of 27 with the dienes (31 and 36) proceeded in completely regioselective manners. Nogarene (4) and 7-deoxynogarol (3) were synthesized from the resulting adducts, respectively.
A resemblance of the molecular shapes between 1,4-diamino-cyclitol aminoglycoside antibiotics such as fortimicin A (1) and 1,6-anhydromaltose (2) prompted us to synthesize a new potential antimicrobial compound with structure analogous to the antibiotics, employing 2 as the starting material. The present paper describes the synthesis of a new 1,4-diaminocyclitol aminoglycoside (3), developing several novel synthetic methodology. The structural characteristic of 3, the absence of an equatorial methoxy group at C-4, regularly present in the natural antibiotics of this kind, resulted in no conformational inversion of the cyclitol moiety into the undesirable one. The following new processes were the particularly novel ones: (i) conversion of 1,6-anhydro-disaccharide to the corresponding phenyl thioglycoside by selective ring fission, (ii) the first application of Ferrier reaction to the thioglycoside for its transformation to a cyclohexanone derivative, and (iii) selective hydrogenation of a C-C double bond without reducing the coexisting azido groups.
1. Synthesis of a common glycan chain of I-active glycolipid. I-Active glycolipid which is the representative of the glycoconjugates carrying lactosamine as a repeating unit contains a common branched glycan chain 1. In order to develop the strategy for the synthesis of such a glycan chain, a lactosamine synthon 2 was designed and synthesized from monosaccharide precursors. The versatility of 2 was demonstrated by the synthesis of the octasaccharide 1. 2. Sulfenate esters as glycosyl acceptors. A novel approach to the synthesis of glycosylated products was developed by the Lewis acid mediated activation of sulfenate esters 15. The reaction of 15 with glycals 16 gave 2-deoxy-2-phenylthioglycosides 18 which are potential precursors of 2-deoxyglycosides. Thioglycosides 17 also reacted with 15 and 0-glycosides 19 were obtained under mild conditions. The stereoselectivity was found to be dependent on the solvent employed. 3. Stereoselective synthesis of α-glycosides of sialic acid. Sialic acid is an important constituent of glycolipids. However, the stereoselective glycosylation of sialic acid is difficult to achieve. In order to solve this problem by neighbouring group participation, we designed 20 which in turn was synthesized from 2,3-dehydro derivative 21. The reactions of 20 with glycosyl acceptors gave α-glycosides exclusively.
Prostacyclin (PGI_2, 1) and its stable analogue, isocarbacyclin 2, have been synthesized from the readily available common intermediate 3. Prostacyclin: Reduction of the C-9 carbonyl of 3 by L-Selectride gives the 9α-alcohol 4 exclusively. The intramolecular alkoxypalladation/depalladation using PdCl_2(C_6H_5CN)_2 and then ammonium formate leads to (Z)-2-alkylidenetetrahydrofuran structure 6 with high stereo-selectivity (5Z/5E > 33: 1). Deprotection of 11- and 15-hydroxyls and alkaline hydrolysis of the ester group complete the synthesis of 1. Isocarbacyclin: Conversion of 3 to the α-silylated alcohol 10 has been accomplished by the following four-step sequence: (1) methylenation of the 9-keto group using a Zn-CH_2Br_2-TiCl_4 mixed reagent, (2) stereoselective hydroboration by 9-borabicyclo[3.3.1]-nonane and oxidative workup, (3) oxidation of the primary alcohol with pyridinium dichromate, (4) silylation of the aldehyde with the reagent prepared by mixing of copper(I) cyanide and 2 equiv of dimethylphenyl-silyllithium. The m-trifluoromethylbenzoate 11 undergoes photochemical radical cyclization in aqueous THF containing N-methylcarbazole and Mg(ClO_4)_2 to lead to the allylsilane 13. The same allylsilane is also accessible by reaction of the xanthate 12 with tributyltin hydride in the presence of di-t-butyl peroxide. Deprotection of 11- and 15-hydroxyls, regiospecific protodesilylation of the allylsilane, and alkaline hydrolysis of the ester group give 2.
DNA serves as a target for the action of small molecules including natural antibiotics and designed synthetic molecules. These molecules bind directry to DNA, in some cases with sequence-specific manner, and cause DNA strand brekage by metal ions dependent reaction. Current interests for the action of these molecules concern with the chemical mechanisms of their sequence-specific recognition and degradation of DNA. Bleomycin, a family of glycopeptide-derived antibiotics, mediate degradation of DNA by metal ions such as Fe(II) and oxygen dependent reaction preferentially at the pyrimidine of 5'-GC-3' and 5'-GT-3' recognition sites. Bithiazole group is considered to play a key role for the BLM binding to double-helical DNA, while its binding mode has not yet been well understood. A critical question is whether bithiazole grop can recognize GC and GT sequences. Photo-BLM and lumi-BLM, which were obtained by selective photo-rearrangement at 2,4'-bithiazole group of BLM to 4,4'-bithiazole and thiazolyl-isothiazole groups, respectively, were shown to degradate DNA at the same sequences as BLM does. Since photo- and lumi-BLMs retain a common positioning of two ring nitrogens in their hetero-aromatic rings and BLMs show the strong affinities to guanine residue in DNA, one interpretation is that the interaction between the guanine and the ring nitrogen(s) may control the sequence specificity in DNA cleaving or binding mode of BLMs. To examine the role of N-2 amino group of guanine residue, we synthesized the oligodeoxynucleotides replacing the G-C base pairs with I-C base pairs. Inosine, like guanine, base pairs with cytosine, but it lacks an N-2 amino group that could protrude into the minor groove of double-helical B-DNA. The question is whether inosine can effect to the cleavage reaction by BLMs. DNA cleavage reactions by these photochemically modified BLMs and the possible interaction between guanine N-2 amino group and BLMs will be discussed.
Bialaphos is a tripeptide produced by Streptomyces hygroscopicus and now being used as herbicide in Japan. It has a very unique C-P-C bond in the phosphinothricin moiety. Its biosynthesis has been revealed in detail by using labeled precursors, appropriate blocked mutants and enzyme inhibitors as summarized in Fig. 4.
The fate of all the carbons and hydrogens originating from MVA were revealed by 13C NMR spectroscopy in the biosynthesis of phytosterols. The 1,2-methyl migrations (14β→13β and 8α→14α) were demonstrated in the formation of cycloartenol (2) in Physalis peruviana callus fed with [1,2-^<13>C_2]acetate. Also the 1,2-hydride shifts (17β→20, 13α→17α, 9β→8β, and 24→25) were verified in 24-methylenecycloartanol (5) biosynthesized from [2-^<13>CD_3]acetate in Trichosanthes kirilowii var. japonica callus by observing β-deuterium isotopically shifted signals. The both C-11 and C-12 of sitosterol (10) biosynthesized in R. japonica callus in the presence of [5-^<13>CD_2]MVA were labeled in two ways, ^<13>CD_2 and ^<13>CDH, showing that squalene is released from the enzyme involved. The following oxidation reaction does not distinguish one farnesyl moiety from the other when forming squaleneoxide (9A) and (9B). In 24α-ethylsterol (6), no deuterium atom around C-24 was observed and the hydride shift (24→25) was detected in the 24-methylene derivative (5). However, in the case of 24β-ethyl-sterols (24) and (26) obtained from T. kirilowii fed with [2-^<13>CD_3]acetate, the C-24 was found to bear a deuterium atom. The C-26 of (25) and C-27 (pro-S) of (27) were observed as doublets labelled from [1,2-^<13>C_2] acetate. These findings suggest that the Δ^<25> double bond in (24) is formed with a hydrogen elimination from the methyl group at C-25 originating from C-6 of MVA, then hydrogen attack on the 25-re-face of the double bond occurs to form (26). The C-27 of this final product is from the C-6 of MVA.
"Monoterpene cyclase" responsible for the cyclization of acyclic allylic pyrophosphate was isolated from the leaves of Mentha spicata and purified about 54-fold by chromatography on a Sephadex G-200 column following by a DEAE-cellulose column. Bivalent metal cations, especially manganese ion, was essential for the formation of allylic cations for the enzymatic cyclization. On the basis of the potential energy of the allylic cations, a reaction path from geranyl pyrophosphate (GPP) to cyclic monoterpenoids was predicted ; this shows that linalyl cation is a preferred intermediate for cyclization of the C_<10>-prenyl chain. Linalyl cation in the process of the enzymatic cyclization was confirmed by conversion of (+)-linalyl pyrophosphate (LPP) to (-)-limonene with the "monoterpene cyclase". Examination of the affinity of several substrates to the "monoterpene cyclase" by means of the UV difference spectrum indicates that the "monoterpene cyclase" can recognize the pyrophosphate moiety and the chain-length and enantiomeric structure of the hydrophobic moiety. In the biosynthesis of cyclic monoterpenoids from C_<10>-prenyl chain precursors by their cyclization, thus, it has been elucidated that GPP is first bound to the active site of the "monoterpene cyclase" with a bivalent metal ion. GPP bound to the active sites is transformed to linalyl cation by pulling out its pyrophosphate moiety with the bivalent metal ion and then the linalyl cation stereospecifically cyclizes to cyclic monoterpenoids under the steric control characteristic of the respective plants.
Phytoalexins are antimicrobial compounds of low molecular weight that are both synthesized by and accumulated in plants after exposure to microorganisms. The role of these compounds as antiparasitic agents in some plants is supported by considerable evidence, but little is known about the mechanisms that control their production. In the course of studies on the isolation of an endogenous elicitor(s) for phytoalexin formation from potato tuber tissues infected with Phytophthora infestans, we assumed that the phytoalexin elicitation has some relationship with active oxygen species, generated from the interaction of diseased plants and air. Experiments on the basis of this assumption have led to the following findings: i) hydrogen peroxide was generated in a detectable amount from the host plant but not from the fungus ; ii) inoculation of hydrogen peroxide induced phytoalexin production ; iii) phytoalexin production was accompanied by the generation of hydrogen peroxide ; iv) "gene-for-gene specificity" was highly dependent on hydrogen peroxide generation. Such dynamic roles of hydrogen peroxide as an endogenous phytoalexin elicitor were further supported with sweet potato and kidney bean.
A sporogenic substance, named sporogen-AO 1, was isolated from the cultured broth of Aspergillus oryzae ; the fungus has been widely used in Japanese fermentation industry for producing Japanese traditional foods (sake, soy sause and miso) and also various useful enzymes. Sporogen-AO 1, isolated from an abundantly sporulating strain, exhibited significant sporulation-stimulating activity at a dose of 4.4μg/paper disc on the sparsely sporulating strain of the fungus. The structure was elucidated as the figure (1) on the basis of spectroscopic analysis. A new unknown sporogenic substance(65μg) has been isolated from the cultured broth(180 liters) of a different strain of Asp. oryzae. Improving the yield as well as its structure analysis is now under investigation.
Model N-linked oligosaccharides chirally deuterated at C-6 were synthesized and ^1H-NMR of the model saccharides were measured in order to clarify the conformational preference about (1-6) glycosidic linkages in aqueous solution. The signals of H-6S and H-6R were discriminated unequivocally in these oligosaccharides and the rotamer populations about C-5-C-6 single bonds (ω angle) were calculated from the values of J_<5,6S> and J_<5,6R>. The preferred conformations of φ and ψ angles were estimated on the bases of the differential relaxation rates and the NOE data. In these branched oligosaccharides, the gg rotamer was preferred and the tg rotamer was negligible. The rotamer populations of ω angle of "bisectGlcNAc" model was different from other branched oligosaccharides. These works provides the experimental evidences to the previous estimation of the conformation about (1-6)glycosidic linkage.
During the past few years we have been attempting to devise microanalytical techniques to determine the position of the glycoside linkages in oligosaccharides based on the exciton chirality method. In the course of these studies we have found the additivity in the amplitudes of split Cotton effects of hexopyranoside p-phenylbenzyl ethers. All 18 di-p-phenylbenzyl ethers of α-methyl glucopyranoside, mannopyranoside, and galactopyranoside were prepared to provide the standard A values of bichromophoric unit. The additivity relation was next tested by making all possible tri- and tetra-glycoside benzylates. Very good agreement was shown between A_<obs> and A_<calc> in all cases. Its application to structure determination of saponin. The Mexican plant Agave lecheguilla yields a variety of new molluscicidal saponins. One of them (AL-3) was perbenzylated with PhBnBr and NaH in DMF/THF/TMU. The analysis of the glycoside linkages was done by methanolysis of the perbenzylate in the microwave oven, subsequent HPLC of the methanolysate, and MS/UV/CD measurements of sugar benzylates. 1,4-Glycosidic linkages were identified in the glucose and galactose groups of AL-3 1.
Chemical investigation of Gelsemium elegans collected in Thailand resulted in the isolation of 6 new indole alkaloids, along with 7 known compounds, i.e. gelsemine(1), gelsevirine(2), koumine (3), gelsenicine(4), 14-hydroxygelsenicine(5), humantenine(6), and 14-hydroxygelsedine(7). The structures of new alkaloids, 16-epi-voacarpine(11), 19-hydroxydihydrogelsevirine(12), 19-(Z)-taberpsychine(15), koumine-N-oxide(16), gelsemine-N-oxide(18), and 19-oxo-gelsenicine(19) were determined by the spectroscopic analysis, chemical reactions, and/or X-ray analysis. Furthermore, structures of two indole alkaloids, "akuammidine" and koumidine, previously isolated from the same plants, were revised to be (8) and (10), respectively. We propose here the biosynthetic route of Gelsemium alkaloids. (Chart2) Intermediate (21) formed from strictosidine (20) will serve as a precursor of sarpagine type alkaloids, such as koumidine (10), which will be further transformed by oxidation and rearrangment into taberpsychine (15), koumine (3), humantenine (25), and gelsemine (1) alkaloids. Intermediate (21) will also be metabolized to C_<21>-norsarpagine type (22), which will be converted to the gelsedine (24) series. In order to support the biogenetic proposal above, we designed the biomimetic synthesis of koumine and humantenine skeletons from gardneria alkaloids. The synthesis of 11-methoxykoumine (30) was accomplished starting from 18-hydroxygardnerine (27) through the intramolecular C-C bond formation between the indole part (C_7) and allylic cation (C_<20>) using Pd catalysis. The biomimetic synthesis of des-N(a)-methoxyhumantenirine (35) was also achieved from gardnerine (16) in a highly stereoselective manner. Thus, OsO_4 oxidation of C/D-ring opening product (31) gave exclusively oxindole (37) which had desired configuration at C_7. (37) was further transformed into (35) via the olefine inversion process and deprotection of N(b) group.
Commelinin and protocyanin are typical metalloanthocyanins. Commelinin consists of 6 molecules each of malonylawobanin (M) and flavocommelin (F), and 2 atoms of magnesium. Electrophoresis data showed the molecular composition of commelinin to be [M_6F_6Mg_2]^<6-> ; molecular weight being about 9,000. We propose a gross structure of commelinin as shown in Fig. 6. Two copigmented MF units are stacked chirally by hydrophobic interaction between two M molecules to form FMMF unit. Three FMMF units are doubly linked by chelation with two magnesium atoms. Using the gross structure as a reference, X-ray data of Cd-commelinin was analyzed ; although the data was not completely solved due to the high molecular weight, six anthocyanidin nuclei could be visualized as shown in Fig. 7. The figure is in good accord with the above gross structure. Protocyanin obtained from blue cornflower, Centaurea cyanus, consists of about 6 molecules each of succinylcyanin and apigenin 4-(6-O-malonylglucoside)-7-glucuronide and one atom each of Fe and Mg. Its gross structure may be very similar to that of commelinin.
The newt Cynops ensicauda collected in Okinawa, Japan, contained tetrodotoxin (TTX)(1) and its new analogs. Two analogs, compound A and B, were isolated by successive treatment of AcOH extracts on columns of charcoal, BioGel P-2, BioRex70, and Hitachigel 3011C gel. From 3.5kg of the newts 120mg of TTX, 18mg of compound A, and 30mg of compound B were obtained. High resolution FAB mass spectra taken on a JEOL JMS-DX-303HF indicated A to have the same molecular formula as TTX(C_<11>H_<17>O_8N_3) and B to be deoxyTTX (C_<11>H_<17>O_7N_3). ^1H NMR spectra of A showed a high field shift of 11-CH_2 suggested the CH_2OH at C-6 to be axial, 6-epiTTX(2) The axial configuration was further confirmed by NOE measurments. Configuration at C-9 was proved to be the same as TTX. Likewise B was assigned to 11-deoxyTTX(3), and its 11-CH_3 was suggested equatorial as same as TTX. Both 2 and I were in a tautomeric equilibrium between hemilactal (2a,3a) and lactone (2b,3b) forms that were confirmed by NOESY measurments which indicated the saturation transfer between two froms.
Commelinin and protocyanin are typical metalloanthocyanins. Commelinin consists of 6 molecules each of malonylawobanin (M) and flavocommelin (F), and 2 atoms of magnesium. Electrophoresis data showed the molecular composition of commelinin to be [M_6F_6Mg_2]^<6->; molecular weight being about 9,000. We propose a gross structure of commelinin as shown in Fig. 6. Two copigmented MF units are stacked chirally by hydrophobic interaction between two M molecules to form FMMF unit. Three FMMF units are doubly linked by chelation with two magnesium atoms. Using the gross structure as a reference, X-ray data of Cd-commelinin was analyzed; although the data was not completely solved due to the high molecular weight, six anthocyanidin nuclei could be visualized as shown in Fig. 7. The figure is in good accord with the above gross structure. Protocyanin obtained from blue cornflower, Centaurea cyanus, consists of about 6 molecules each of succinylcyanin and apigenin 4-(6-O-malonylglucoside)-7-glucuronide and one atom each of Fe and Mg. Its gross structure may be very similar to that of commelinin.
Structure 1 was proposed for sulfomycin I, an antibacterial peptide antibiotic produced by Streptomyces viridochromogenes subsp. sulfomycini ATCC 29776. In addition to the sub-units a-d assigned earlier, the incorporation of the sub-units e-i in 1 was established based on the structures of mild acid hydrolysis products (2a, 2b, 3a, and 4a, 4b) of the intact antibiotic. These sub-units were connected by using the results of long-range ^<13>C-^1H couplings and NOE (Fig. 1) summarized in Charts 4 and 5 to give the novel macrocyclic structure 1. ^1H and ^<13>C NMR data fully analyzed by various 2D techniques supported the structure. It was also suggested that structurally related peptide antibiotic, berninamycin, should contain the sub-unit h instead of berninamycinic acid moiety assigned previously.
Antibiotic, dityromycin was isolated from the culture broth of Streptomyces sp. strain No. AM-2504. It is active against Bacillus, Corynebacterium, and Clostridium, but inactive against Staphylococcus aureus and Gram-negative bacteria. Dityromycin was determined to have a molecular weight of 1288 by FAB-MS, and to be composed of N-MeVal (2), Pro (2), Val (1), phenylglycine (1), and CH_3NH_2 (1) (6M HCl, 140℃, 40h). In addition, N,N-Me_2Thr-Val-OH (1) was isolated from the hydrolyzate with 6M HCl (110℃, 24h) and di-α-amino acid (3) containing diphenylether and γ-hydroxyisoleucine lactone (4) were obtained by reductive hydrolysis with 57% HI-P (110℃, 24h). The sequence of peptide fragments, 5 and 6, obtained by alkaline treatment (1M NaOH, r.t., 3h) were clarified by partial hydrolysis, selective cleavage, and Edman degradation. Moreover, another fragment peptide 7 whose structure was determined as shown in Fig. 4 was derived by partial acid hydrolysis (cHCl-AcOH (1: 1), 37℃, 3h). From the comparison of 7 with dityromycin (Table 5), the total structure could be deduced as shown in Fig. 6. Dityromycin was clarified to have unique structure which includes bicyclic depsipeptide, epoxide, diphenylether and so on.
We propose the structure of a nucleoside antibiotic liposidomycinB(1), which is a main component produced by Streptomyces griseosporeus, as shown in Fig. 1 on the basis of chemical and spectroscopic evidences. Liposidomycins strongly inhibited the lipid cycle of peptidoglycan synthetase prepared from E. coli (ID_<50> 0.03μg/ml). It is interesting that there is the structural similarity between 1 and the lipid intermediate (Undecaprenol-UDP-MurNAc-pentapeptide).
A novel antibiotic, aurantinin has been isolated from the cultured broth of Bacillus aurantinus. The antibiotic shows a potent antimicrobial activity against Gram-positive bacteria, especially anaerobes. The structures of aurantinins A and B were assigned by biosynthetic means using feeding experiments of ^<13>C labeled precursors including 2D-NMR and LSPD studies. Aurantinins are a novel skeleton containing four rings, a triene and an acid unhydride moiety. The antibiotic also possesses an unusual polyketide skeleton which we never find out such a biosynthetic building unit in a secondary metabolite from actinomycetes and fungi.
In connection with our continuing studies on bioactive substances from the Japanese marine organisms, we have isolated three new diterpenoids, stolonidiol (1), stolonidiol monoacetate (2), and the compound 3, from the soft coral (Clavularia sp.) as the major secondary metabolites. The compound 1 and 2 showed a strong cytotoxic activity against P388 leukemia cells in vitro (IC_<50> 0.015μg/ml for each compound). The plane structures of 1 and 2 were elucidated on the basis of chemical reactions and two-dimensional (2D) NMR spectra (^1H J-resolved spectrum, ^<13>C-^1H COSY, COLOC, and INADEQUATE). The relative stereochemistries were determined by measurement of high dilution IR spectrum and 2D NOESY, and the absolute stereochemistries were elucidated by CD measurement of the derivative 8. The X-ray crystallographic analysis of the derivative 10 confirmed the full structures of 1 and 2. The structure of 3 was also deduced on the basis of chemical reactions and spectroscopic data. The structures of 1 and 2 are characterized by new bicyclo-[9.3.0]tetradecane skeleton having the cis stereochemistry between the methyl group at C-1 and the alkyl group at C-12, which is different from that of the dolabellane-type bicyclic diterpenoids.
A cyclic depsipeptide dolastatin 11 (1) was isolated as the major antineo-plastic component of the sea hare Dolabella auricularia, collected in the Indian Ocean. Dolastatin 11 has shown antineoplastic activity against the PS leukemia, ED_<50> 2.7×10^<-3>μg/ml. Detailed studies on the 400MHz 'H-'H-COSY, 2D-J resolved, 'H-^<13>C 2D-shift correlated and 'H NOESEY experiments combined with 'H NOE difference NMR and SP-SIMS experiments, (in addition to acid and base hydrolysis studies, followed by GC-MS analysis) were employed to elucidate the structure of dolastatin 11 (1). Interestingly, structure (1) was close to that of Majusculamide C, which was isolated from the blue-green algae Lyngbya majuscula and structure determined by R. Moore and colleagues in 1984. The difference resided in replacement of a N-methylisoleucine unit in Majusculamide C with a N-methylleucine in dolastatin 11 (1). In order to confirm the proposed pentapeptide portion of structure (1), the synthesis of the segment Gly-NMe-L-Leu-Gly-NMe-L-Val-OMe-NMe-L-Tyr-OMe (8) was completed. The synthetic pentapeptide (8) was useful in confirming the dolastatin 11 structural determination.
During the course of our search for bioactive metabolites from Japanese marine invertebrates, we found that methanol extract of a sponge Theonella sp. collected in Hachijo-jima island revealed strong activity both in the echinoderm egg assay and in the cytotoxicity test. Fran this sponge we have isolated two active components, named bistheonellides A and B (1 and 2, respectively), which inhibited development of starfish embryos at 0.1 and 0.2μg/ml, respectively as well as growth of tumor cells at low concentrations. Bistheonellide A exhibited spectral data, except for molecular weight, identical with those for misakinolide A which had been reported from an Okinawan Theonella sponge. Direct comparison showed that both compounds were identical. On the basis of FABMS, molecular weight determination by vapor pressure method, and NMR analyses of octaacetyl and p-bromobenzoyl derivatives, bistheonellide A (misakinolide A) was revised from the previously proposed monomeric macrolide (3) to its dimeric macrodiolide (1). This was also confirmed by chemical degradation work. Similarly, bistheonellide B was found to have structure 2 by spectral and chemical analyses.
An antifungal compound, goniodomin A, was isolated from the dinoflagellate Goniodoma pseudogoniaulax collected in the rock pool at Jogashima, Kanagawa Prefecture. It showed the antifungal activity to Mortierella ramannianus at a concentration of 0.5μg/ml, and inhibited the cell division of fertilized sea urchin eggs at 0.05μg/ml. Goniodomin A was supposed to be closely related to the goniodomin which was isolated from Goniodoma sp. by Sharma et al. in 1968 but of which structure remained undetermined. We decided the gross structure of goniodomin A(1) as a novel polyether lactone, based on the ^1H-^1H COSY, 2step RCT COSY, ^1H-^<13>C COSY, COLOC and PSNOESY.
Recently marine micro-organisms have proved to be a new valuable source of bioactive substances, since some symbiotic micro-organisms associated with marine animals have been demonstrated to be responsible for the production of some marine natural products. Neurotoxins from symbiotic dinoflagellates are now used as essential tools in understanding the moleculalr basis of cellular excitability. During our studies on bioactive metabolites from marine organisms, we have successfully cultivated a dinoflagellate Amphidinium sp. isolated from an Okinawan flatworm Amphiscolops sp. and now isolated three novel macrolides, amphidinolide-A (1), -B (2), and -C (3) from the extract of this dinoflagellate. Their structures were elucidated on the basis of extensive spectroscopic analyses, especially by the combination of recently developed 2D NMR methods such as HMBC (^1H-detected heteronuclear multiple-bond correlation) experiment. It seems interesting that these three macrolides (1-3) with different structural and biological features were obtained from the same dinoflagellate. Amphidinolide-A, -B, and -C showed strong antineoplastic activity against L1210 murine leukemia cells with IC_<50> values of 2.4μg/mL, 0.14ng/mL, and 5.8ng/mL, respectively.
As one of continuous studies on naturally occurring spiro compounds, we describe synthetic studies on chamigrane typesesquiterpenes. Key features of this report are 1) construction of the basic spiro[5.5]undecane skelton by the metal salt catalyzed decomposition of the phenolic α-diazoketone, 2) synthesis of (±)-α-chamigrene (8) starting from the spirodienone 5, 3) effects of the neighbouring hydroxy group in the Birch reduction of cross conjugated dienones, 4) synthesis of the bromochamigrane derivative Z-22 starting from the enone 14, and 5) synthesis and structure of the rearranged bromochamigrane derivative 23.
Two sex pheromones of the American cockroach, periplanone A and B, have been isolated by Persoons et al. The structure of the latter was proposed by the same authors, and then its stereostructure including the absolute configuration was unambiguously determined by its synthesis. Furthermore, the structure (1) of periplanone A has been proposed by Persoons et al., on the basis of its spectral data together with some chemical evidence, but the stereochemistry was not known. In order to elucidate the structure of periplanone A, the authors have synthesized two possible hydroazulenones (5 and 6) from germacrene-D by using biomimetic transannular reactions as a key step. However, the spectral data of synthetic compounds were entirely different from those of natural one. Therefore, the ^1H NMR and IR spectral data of periplanone A and its rearrangement product were reexamined, consequently, the structures of both compounds were found to be resembled each other. Clearly, the structure of periplanone A, which is quite labile as compared with the rearrangement product, seems to be represented by one of the possible decalones (I or II), while the latter must be depicted by III or IV. As shown in Table 1 and 2, the coupling constants based on the conformations I and III, obtained from molecular mechanics calculations, were compatible with the observed ones for periplanone A and rearrangement product, respectively. Thus, the stereostructure of periplanone A was elucidated as I.