A new pathway to DNA oligomers of unprecedently high purity has been opened using allyl and allyloxycarbonyl (AOC) groups as protectors of internucleotide linkage and nucleobases, respectively, in conjunction with palladium chemistry. The efficiency of this method has been demonstrated by the synthesis of a 60mer d(^5'TA TGGGCCTTTTGATAGGATGCTCACCGAGCAAAACCAAGAACAACCAGGAGATTTTATT^3') known as a part of a DNA sequence of yolk sac tumor proteoglycan cDNA pPG1. The synthesis has been performed on controlled pore glass supports with a long-chain alkylamine spacer via the phosphoramidite method using monomer units in which all NH_2 moieties of 2'-deoxyadenosine, 2'-deoxycytidine, and 2'-deoxyguanosine are blocked by AOC groups and the phosphoramidite functions are protected by allyl groups. The coupling reaction proceeds in 99.3% average yield, attaining 66% overall yield. The fully protected product is deblocked by treatment with a mixture of tris(dibenzylideneacetone)dipalladium(0) chloroform complex (2.5 equiv/allyl), triphenyl-phosphine (25 equiv/allyl), and a large excess of butylamine and formic acid in THF at 50℃ for 1h, and then with sodium N,N-diethyldithiocarbamate solution for 0.5h. The target DNA is detached from the polymer supports by exposure to conc ammonia at room temperature for 2h. The autoradiogram and bio-image chromatogram of the ^<32>P-labeled 5'-phosphrylated product reveal that the 60mer possesses extremely high purity (70% content in the crude product) which is unaccessible by the conventional method using as protecting groups acyl for amino function of nucleobases and 2-cyanoethyl for internucleotid linkage (20% content).
The biological activities of Neocarzinostatin and Esperamicin; antitumer biotics, are induced by DNA scission via a proposed mechanism that involves the hydrogen absorption from the phosphate backbone of DNA by the diradicals 3 and 6 produced from the strained intermediates 2 and 5 respectively. Now we synthesized the highly strained 9-membered intermediate 7 using transannular (2,3)-Wittig rearrangement of 12-membered allyl propargyl ether 10, which was obtained by the intramolecular O-alkylation of bromohydrin 11. NCS skeleton 8 was introduced by the dehydration of tertiary alcohol of 7, and Esperamicin model 9 was obtained by the dehydration of secondary alcohol of 7. The diyne 9 led spontaneous Bergman cyclization providing 18.
Neocarzinostatin(NCS) Chromophore analogues 7, 8 and 9 were synthesized and their chemical behavior was examined in order to answer the questions: (i) Is the ring strain inherent in the unsaturated 9-membered ring system essential to such novel molecular transformation as NCS Chromophore 1 does?; (ii) Is the epoxide functionality also essential to it?; (iii) Is there any other mode of aromatization besides Myers' type? The results demonstrated that even the dienediyne system which has not epoxide functionality nor severe ring strain, such as 7-9, can undergo the radical initiated molecular transformation to tetrahydrobenzindans in addition to Myers' type nucleophile induced aromatization. This suggests the importance of free radical triggering mechanism in the aromatization of 1. The research on this issue is currently under way.
In our study on the isolation and structure elucidation of biologically active compounds from marine invertebrates, we synthesized the four diastereomers of C_<16>-phytosphingosine (10, 12, 25, and 26), acanthacerebroside A (1), and D-galactosylceramide (3b) as described below. (2S, 3S)-Allylic alcohol, which was prepared from the L-serine derivative and the (E)-vinylalane compound, was converted into (2S, 3S, 4R)- and (2S, 3S, 4S)-phytosphingosines by epoxidation, DIBAH reduction, and debenzylation. The same treatment of (2S, 3R)-allylic alcohol gave (2S, 3R, 4R)- and (2S, 3R, 4S)-phytosphingosines. (2R)-Acetoxytetracosanoic acid was prepared and coupled to (2S, 3S, 4R)-phytosphingosine to give the ceramide (34). Glycosylation of 34 gave the desired monoglycoside (36) and the bisglycoside (37). 36 was converted into 1 by deacetylation. New D-galactosylceramides were isolated from Chondropsis sp., but the absolute stereochemistry has not been determined. Therefore, (2S, 3S, 4R, 6E)- and (2R, 3R, 4R, 6E)-phytosphingosines were prepared via asymmetric epoxidation. The former was transformed to (2S, 3S, 4R, 6E, 2'R)-D-galactosylceramide and its heptaacetate. The spectral data of them were in excellent agreement with those of the natural specimens.
Glycosphingolipids (GSL) present on cell surface are believed to play imortant physiological roles for cell surface molecular recognition mechanisms. In order to supply enough amount of chemically well characterized GSL for biochemical as well as biophysical studies, it is prerequisite to develop synthetic routes to such molecules with high stereo- and regio-control. From such view points, our projects on synthetic studies on GSL has started several years ago. As part of these projects, we describe here for the first time total synthesis of globo-series glycopentaosyl GSL 1 and 2, so-called SSEA-31,2 and Para-Forsmann3 antigen, respectively. Retrosynthetic analysis of 1 and 2 is depicted in scheme 1. A) Synthesis of SSEA-3 (1) Boron trifluoride etherate promoted glycosylation of glycotriosyl acceptor 5 with trichloroacetimidate 6 gave a 22% yield of the desired glycopentaoside 7 which was futher converted into a glycosyl donor 11 in 4 steps. Crucial coupling between 11 and 3 did afford 12 in 33% yield which was deprotected to give 1. Synthetic 1 was completely identified with natural 1 through comparison of their ^1H-nmr data. B) Synthesis of Para-Frossman antigen 2 Glycosylation of alcohol 15 with bromide 14 gave a 94% yield of 16 which was converted into 18 in 39% overall yield in 4 steps. Compound 18 was converted into a glycosyl donor 23 which was coupled with 5 to give as high as a 58% yield of the desired 29 in the presence of (Bu_4N)_2CuBr_4-AgOTf in CH_3NO_2 at 0°. Conversion of 29 into a glycosyl donor 35 was successfully achieved and crucial coupling with a glycosyl acceptor 4 gave about 50% yield of the desired 37 which was further transformed into a target 2 in a conventional manner. In summary, first total syntheses of both 1 and 2 were achieved by use of a common glycotriosyl acceptor 5.
A very simple procedure of O-glycosidation has been developed without using any metal salt. After dried up the reaction system containing cholesterol (5) and benzylated glucosyl chloride 1 (1.2 equiv) along with tetramethylurea (1.2 equiv) in dichloromethane by using apparatus I, the concentrated mixture was heated at 120℃ for 2h affording α- and β-glycosides (60:40) in 92% yield after silica gel column chromatography. Glycosyl chlorides 2, 3, and 4, are also employed for glycosyl donor toward a variety of primary and secondary alcohols. Although this procedure provides glycosides non-stereoselectively, glycosidation with rhamnosyl chloride 4 takes place stereospecific manner to give rise to α-rhamnoside as seen in Table I. Although wide attention have been focussing to the inclusion chemistry of cyclodextrins, synthesis of cyclooligosaccharides have been reported only in few cases. Herein we disclose an novel synthesis of the first L-series cyclooligosaccharide by means of stereoselective thermal glycosidation of rhamnosyl residue. The thermal glycosidation of 15 with 17 in the presence of TMU gave a dimer 18 in 64% yield. The dimer 19 derived from 18 was condensed with 17 under thermal condition to give trimer 20 in 62% yield. Condensation of trimer chloride 21 and trimer alcohol 22 at 120℃ for 2h afforded a hexamer 23 in 24% yield. Cycloglycosidation of hexamer 24 under thermal condition took place smoothly to give the first L-cyclooligosaccharide 25 in 77% yield.
From leaves of Stevia rebaudiana, the major sweet principle, stevioside(S) has been isolated together with rebaudioside A (RA) and several other minor sweet glycosides (Table 1). From leaves of Rubus suavissimus, the homologuous sweet glycoside, rubusoside (RU) has been isolated(Table 1). A number of more glucosylated compounds were prepared from S, Ru and their derivatives by trans-1,4-α-glucosylation with starch and cyclodextrin-glucosyltransferase (CGTase) (Tables 2,3 and Fig. 1). Evaluation of sweetness of these products revealed that elongation of 13-O-glycosyl moiety (total: 3 or 4 glucosyl units at 13-OH) resulted in remarkable improvement of the sweetness, while compounds with more glucosyl units in this moiety (total: 5 or 6 glucosyl units) exhibited rather worse sweetness. An increase in glucosyl units at the 19-position led to a change in the sweetness for the worse. Selective synthesis of the good sweeteners found in the above study was schieved by using a galactosyl group as a blocker against the transglucosylation with starch and CGTase (Figs. 2, 3).
In connection with the stereochemical studies of sporaviridin, a polyol macrolide antibiotic, we have developed a convergent general protocol for syn-1,3-polyol synthesis. The method is extendable to higher homologs of this series by repetition. Using this new method, total synthesis of 4,6,8,10,12,14,16,18,20-nonamethoxy-1-pentacosene (3), isolated from blue-green alga Tolypothrix conglutinate var. chlorata, has been accomplished in 21 steps from the ketone (7). Second, a new method for the preparation of anti-1,3-polyol has been developed using a chiral building block (6), a chiral epoxide (22), and LiAlH(O'Bu)_3-LiI reduction. The LiAlH(O'Bu)_3-LiI reduction is a useful method for preparing 1,3-anti-3,5-syn-triol units from B-alkoxy-B-hydroxy ketones with anti-relationship of the alkoxy and the hydroxy groups. The selectivity of the rduction is anti:syn=95:5. Finally, combination of the syn- and anti-1,3-polyol syntheses culminated in establishing a new stereodivergent synthesis of 1,3-polyols containing syn- and anti-1,3-diol units in the chain and four diasteroisomeric polyols (43), (44), (45), and (46) were synthesized in a stereocontrolled manner. Since the present technology could provide facile access to 1,3-polyols by the combination of chiral epoxides, enantiomeric dithianes of (6), and reducing agents of LiAlH_4-LiI and LiAlH(O'Bu)_3-LiI, the flexibility of the reaction sequence in preparing any desired stereo-chemical combination is considerably enhanced.
Since the identification of platelet activating factor (PAF) as alkylacetylglycerophosphocholine, PAF have attracted a great deal of attention in the field of biochemistry, and are now recognized as important chemical mediators for the development of potent new therapeutic agents. We established an efficient route to PAF from tartaric acid. Then, molecular design were carried out in such a way as to lock or localize the conformation of PAF by introducing methyl group in the glycerine moiety, bringing a selective agonist, 1S-Me-PAF. The result also indicates that chemical modification is interesting to start with C-I of the glycerine backbone, and bringing a strong agonist, a cis-disubstituted tetrahydrofuran derivative, partially confined in a ring. The unstable conformation of the agonist further suggests to look for 7-oxabicyclo[2.2.1]heptane derivatives. They turns out to be strong antagonists. The conformationally restricted model approach has opened up a new avenue to the antagonists for PAF.
New approaches to stereocontrol over contiguous chiral centers are described which rely on the intramolecular ene reactions. (1) Acetylene ene-cyclizations proceed with high level (>90%) of trans diastereofacial control even over the quaternary centers. (2) The olefin ene-cyclizations involving Z-ene component have been found to proceed with high level (97%) of stereocontrol over three contiguous chiral centers by the combination of diastereofacial selection (97%) and intraanular diastereoselection (100%). (3) The olefin ene-cyclization involving trisubstituted enophile component provides an efficient approach to stereocontrol over four contiguous chiral centers. Its utility is illustrated through the short synthesis of iridoids. Thus, the stereocontrol over up to four contiguous chiral centers can be attained by the convergent combination of diastereofacial selection and intra- and extraanular diastereoselections.
A novel method to replace the bridgehead ether group of 1-methoxybicyclo[2.2.2]oct-5-en-2-ones (12) by an alkyl or aryl group or hydrogen has been developed. By treatment with BF_3-2MeOH, ketones 12 were transformed into 1-methoxybicyclo[3.2.1]oct-3-en-2-ones (13). Reactions of 13 with organolithium reagents (RM) gave the endo alcohols (15). By treatment with TsOH in benzene, pinacol-type rearrangement of 15 proceeded smoothly to give the C-1 substituted bicyclo[2.2.2]oct-5-en-2-ones (17). The C-1 unsubstituted bicyclo[2.2.2]octenones (17, R=H) were derived similarly using DIBAH instead of RM. The overall transformation proceeded in a range of 20-68% yields. This bridgehead substitution has been applied to the first total synthesis of (+/-)-nakafuran-8 (7), antifeedant against common reef fishes isolated from the marine sponges Dysidea fragilis and etheria and some nudibranchs, and to the formal total synthesis of (+/-)-gymnomitrol (25), the unique tricyclic sesquiterpene.
By the cyclobutane ring cleavage, nopinone (1) gives a cyclohexanone bearing an isopropyl unit at its C(4) position. This cleavage reaction is highly usefull in natural product synthesis employing derivatives of 1 as chiral starting materials, provided that the cleavage occurs without loss of optical purity. We first examined the cleavage reaction of cis-3-methylnopinone (2) employed as a model. It was found that the cyclobutane ring of 2 regioselectively underwent the cleavage reaction to provide iodoketone 6 with trimethyiodosilane and diacetate 7 with BF_3・Et_2O-Zn(OAc)_2-Ac_2O with almost no loss of optical purity, respectively. Synthetic approach to penlanfuran (12): 1 was converted to diacetate 15 by employing the above BF_3-OEt_2-Zn(OAc)_2-Ac_2O conditions, and the product 15 was then transformed into (R)-(-)-cryptone (14) through an efficient four-step sequence (Scheme 1). While the Michael addition of a 3-(furyl)methyl magnesium chloride to 14 was unsuccessful, 14 was converted to 24 via oxaspiropropane derivative 23 according to the Tanis's procedure (Scheme 2). Conversion of 24 to 12 is currently under investigation. Synthesis of (+)-β-elemenone (26) and an elemenolide 42 via the common intermediate 28: β,β-Disubstituted nopinone 27 was prepared from 1 through a seven-step sequence showen in Scheme 3 in 27% overall yield. The product 22 was then submitted to the cyclobutane cleavage with the same combination of reagents as above to give 28 directly. The lithium enolate derived from 28 was proved to be amenable to regioselective alkylation process, leading to alcohol 37 with acetone, while keto ester 38 with methyl bromoacetate. (+)-β-Elemenone (26) was obtained from 37 by dehydration, while synthesis of an elemanolide 42 from γ-lactone obtained from 38 is now in progress.
The taxane diterpenes (e.g. taxusin (2), isolated from various species of Taxus, have the unique tricyclic carbon skeleton. Some of them (e.g. taxol (1) are expected to be anticancer agents. Due to the biological importance and unusual structural feature, the synthesis of taxane diterpenes is extensively studied. Herein, we wish to describe the first synthesis of taxane ring system having correct absolute configuration. Our strategy involves the intramolecular Diels-Alder reaction of triene c to form tetracyclic compound b, and the base-induced C-C bond fragmentation reaction of b affording carbon framework of taxanes as the crucial steps (Fig I). The synthesis of taxane ring system 28 was succeeded stereo-selectively as shown in Scheme III. Sequential Michael reaction of kinetic enolate of (+)-carvone with α,β-unsaturated ester 4, prepared from D-mannitol, gave bicyclo[2.2.2]octane derivative 5. The compound 5 was converted into triene 24 via acetal 6, methyl ketone 20 and butenolide 22. Intramolecular Diels-Alder reaction of 24 by heating at 270℃ afforded tetracyclic compound 25 with requisite configuration at C(3) and C(8). Then 25 was transformed into mesylate 26 by two step sequence. The cleavage of C(9)-C(14) bond in 26 was successfully carried out by treatment of 26 with sodium methoxide in methanol to give tricyclo[9.3.1.03,8]pentadecane derivative 27. The optically active 28 having taxane ring system was synthesized by decarboxylation of 27.
A highly efficient eight-membered ring cyclization enabled us to construct taxane carbon framework containing appropriate functionalities for synthesis of natural taxane families. Diketone 16 was prepared eventlessly in 5 steps from manisaldehydedimethylacetal 10. Regioselective silylation, followed by Peterson olefination, afforded cyclization precursor 24. TiCl_4 induced eight-membered ring cyclization occurred rapidly at law temperature to give 26 in 84% isolated yield. The overall yield from the starting material 10 was 33% (8 steps). Interestingly, no intermolecular coupling product was observed though the reaction was performed in 0.1M solution. It should be noted that the tricycle 26 was a single stereoisomer with the same stereochemistry with natural taxanes. We are currently pursuing a total synthesis of taxusin by applying this methodology.
Some potentially useful chiral building blocks bearing bicyclo[2.2.1]heptane framework utilizable enantiodivergently have been prepared in optically pure forms from D-mannitol by chemically and from dicyclopentadiene by enzymatically. Owing to their rigid framework and high functionality, chemical transformations could be carried out efficiently in highly stereo-controlled manners. Moreover, their latent symmetric structures allowed enantiodivergent synthesis of the target molecules. Potentiality of the chiral synthons thus prepared has been demonstrated by establishing enantiocontrolled routes to the following compounds: α-yohimbane indole alkaloids, (-)-nitraraine, (-)-dihydronitraraine, a key prostaglandin intermediate, (4S,5S)-4,5-dihydroxy-4,5-O-isopropylidene-2-cyclopenten-1-one, sandal oil sesquiterpenes, (+)- and (-)-β-santalene, (+)- and (-)-epi-β-santalene, a cuparene type sesquiterpene, (+)- and ()-α-cuparenone, the first simple benzomorphane type alkaloid, (+)- and (-)-aphanorphine, and a calabar bean alkaloid, (+)- and (-)-physostigmine. The present synthesis did not support the proposed structures for nitraraine and dihydronitraraine. Proposed relative structure of (-)-aphanorphine was first confirmed by the present synthesis which also established the absolute structure of the first simple benzomorphane natural product which remained undetermined.
Atisine (1), isolated from Aconitum heterophyllum, was synthesized via intramolecular double Michael reaction as the key step. The azabicyclo[3.3.1]nonane (5) corresponding to AE part was prepared by double Mannich reaction. The diol (11), derived from 5, was subjected to lipase-catalyzed irreversible transformation to give the (-)-acetate (15) in 100% ee. The absolute configuration of the enantiomer (13) of 15 was determined by X-ray analysis of the perchlorate of (+)-camphorsulfonate (19). The stereoselective introduction of hydrogen atom at the C-9 position of the exoolefin (21) was achieved by hydroboration carried out in the presence of BF_3・OEt_2. The substrate (30) of the intramolecular double Michael reaction was effectively synthesized by further manipulation using Wittig reaction and Birch reduction. The annulation of 30 was performed by action with lithium hexamethyldisilazide and the desired pentacyclic compound (32) was obtained as a single stereoisomer. The unnecessary methoxycarbonyl group of 32 was removed by Barton's free radical decarboxylation procedure. Exchange of the N-protecting group furnished the (-)-acetamide (2) which had been converted to atisine (1) by Pelletier. Thus total synthesis of the naturally occurring form of atisine (1) was achieved in a highly enantioselective manner.
Mitomycins are an important class of antitumor antibiotics that have unique structural features. Our synthetic approach toward mitomycins includes the transannular cyclization of the eight-membered intermediate 1 at the later stage of the synthesis. The eight-membered lactam 4 which had been prepared by the reaction called "controlled crisscross annulation" was converted to p-quinone 12 by taking the advantage of the reactivity difference of the conformational isomers 9A and 9B. p-Quinone 12 was transformed into allylic alcohol 14 in 5 steps. Stereospecific introduction of aziridine ring onto the eight-membered ring was accomplished in high yield by the use of intramolecular cyclization reaction. Namely, iodocyclization of allylic carbamate 15 followed by methanolysis afforded aziridine 17 as a single diastereoisomer. The stereochemistry of aziridine 17 was determined by single X-ray crystallographic analysis. Treatment of ketone 18 with TBDMSOTf in the presence of Net_3 gave the cyclized product 19 in quantitive yield. It is noteworthy that this transannular cyclization reaction proceeded without elimination of the oxygen functional group at the bridgehead. Debenzylation of the compound 19 followed by oxidation smoothly provided p-quinone 20 in good yield. Deprotection of p-quinone 20 afforded decarbamoyloxymitomycin derivative 22, which has p-quinone, aziridine and hydroxy group in the molecule.
Eudistomins (1) have been isolated from colonial tunicates and display antiviral activity. We have synthesized these eudistomins which established the absolute configuration. Reaction of N-hydroxytryptamines (2) and protected L-cysteinals (3) gave optically active nitrones (4) in good yields (Table I). When 4 (R_1=H) was treated with TFA-CH_2Cl_2 at room temperature for a few mins, the tetracyclic compounds (5) were obtained as the major product along with the β-carbolines (6) (Table II). The β-carbolines (6) were obtained as the sole product with high selectivity for 6β when the reaction was carried out at ?78℃. In contrast, 4 (R_1=Me) gave the corresponding tetracycles 5 regardless of the reaction temperature and noβ-carboline was obtained. The tetracyclic compound (R1=H) can be transformed to the correspondingβ-carboline with TFA-CH-2Cl_2. Theβ-carboline (6aβ, 6eβ) was cyclized with NCS-CCl_4 to give the desired oxathiazepine (9b, 4%). As an improved cyclization, the reaction of the sulfoxide (10a) with TsOH gave the oxathiazepine (9a) in 21% yield. The enantiomer of debromoeudistomin L (1a) was obtained by deprotection of 9b. The nitrone obtained from 2a and D-cysteinal gave the natural (-)-1a by the similar reactions. On the other hand, the bromination of the tetracyclic compound (5e) gave the bromo derivative (14) selectively. Ring transformation of 14 with TFA gave theβ-carboline (24α), which was further converted to (-)-eudistomin L (1b) by analogous reactions. Other eudistomins (1e, 1f) have also been synthesized by the similar reaction of D-cysteinals with 6-bromo-, and 6-bromo-5-methoxy-N-hydroxytryptamines, respectively.
In our continuing study on thallium compounds, such as (3-formylindo1-4-yl)thallium (8a) and (1-acety1-2,3-dihydroindo1-7-yl)thallium bis(trifluoroacetate) (8b), we have elaborated various new regioselective reactions which enable us to convert C-T1 bond in 8a and 8b either to C-C, C-Si, C-X, C-OH, C-N_3, C-NO_2, or C-SCN bond according to our own will. Utilizing above mentioned reactions, the first total synthesis of indole alkaloid, bipolaramide ((-)-5), was achieved in 47% overall yield starting from commercially available (2S)-(-)-2,3-dihydroindole-2-carboxylic acid ((-)-18) in three (or two) steps. Some derivatives, ((-)-22a-c), having dihalogeno or dialkenyl substituents at the 4 and 11 positions of (6aS)-cis-6a,7,13a,14-tetrahydropyrazino[1,2-a:4,5-a']diindole-6,13-dione were also readily prepared.
In our continuing studies of synthesis of Amaryllidaceae alkaloids, an alternative synthesis of (±)-lycorine was accomplished. Intramolecular Diels-Alder reaction of triene-ester(6) gave cis-δ-lactone(7a) in 86% yield, which was converted to 10 in six steps. Jones oxidation of 10, followed by Curtius rearrangement afforded a carbamate(12), which was treated with TFA and succesively with NaOMe to give 13 in good yield. Epoxidation of t-butyldimethylsilyl ether of 13 proceeded stereoselectively to give 16 as a sole product. In desilylation of 15 with n-Bu_4NF, Payne rearrangement occurred to give two isomeric epoxy-alcohols(16a,b), acetylation of which afforded 17a and 17b, respectively. The same rearrangement was observed in the reaction of acetate(17a) with aq. K_2CO_3 in MeOH. Furthermore, 17b was converted to 18a by the treatment with phenyl selenide. Deselenylation of 18a in a usual manner afforded 19. Although attempts to construct a B ring by cyclization of 19 was fruitless, cyclization of 18a by N-hydroxy-methylation, followed by TFA treatment gave 22. Finally, 22 was treated with NalO_4 to give 23, whose ^1HNMR spectrum was identical with that of an authentic sample prepared for conversion to (±)-lycorine by Sano et al.
Kifunensine(1) was isolated as a new immunomodulator with α-mannosidase inhibitory activity from an actinomycete, Kitasatosporia kifunense Na 9482. Its structure was deduced by detailed ^1H and ^<13>CNMR experiments and confirmed by X-ray crystal analysis. Kifunensine(1) corresponds to a cyclic oxamide derivative of 1-amino-substituted mannojirimycin. This unique structure of 1 prompted us to exploit the syntheses of 1 and 8-epi-kifunensine(3) related similarly to nojirimycin(5). Initially, construction of the simplest octahydro-2, 3-dioxoimidazo [1,2-a] pyridine system 11 consisting of the basic framework of 1 was investigated and this was achieved by a double cyclization of oxamide-aldehyde 9 to 11 with NH_3-M_2OH. Adoption of this method, as a key step, starting from D-mannosamine(13), led to an enantioselective synthesis of kifunensine(1) as shown in scheme III. The reaction probably proceeded via such a route as depicted in Scheme IV. For the synthesis of 8-epi-kifunensine(3), a similar cyclization of oxamide-hemiacetal 29 was attempted. How ever, the reaction never went to the desirable direction. On the other hand, when this cyclization was examined using 2, 4-dimethoxybenzylamine, the desired cyclization product 30 was obtained in a stereoselective manner. Oxidative removal of the benzyl group in 30 provided 8-epi-kifunensine(3) whose structure was confirmed by X-ray crystal analysis.
L-Glutamic acid (Glu) has received much current attention because it is an excitatory neurotransmitter in the mammalian central nervous system and because it is a potent excitotoxin which causes various acute and chronic brain diseases. It is suggested that Glu receptors are classified into three subtypes; N-methyl-D-aspartic acid (NMDA), kainic acid (KA), and quisqualic acid (QA) receptor subtypes. It is reasonable to assume that Glu has different conformations (extended or folded) which fit to the different types of glutamate receptors. We approached this problem by designing four diastereoisomers of L-α-(carboxycyclopropyl)-glycines (L-CCG-I-IV) in which the cyclopropyl group constrains the Glu carbon chain to the extended form or to the folded form. The syntheses of L-CCGs were carried out using efficient methods starting from chiral amino acids: (1) cyclopropanation of (2S)-2-amino-3-butenol derivatives for the syntheses of all L-isomers; (2) intramolecular cyclopropanation of 4 for L-III; and (3) cyclopropanation of an α,β-unsaturated-γ-lactam 10 for L-III and δ-lactone 13 for L-IV. In addition, D-CCG-I-IV were synthesized using the method (1). Neurophysiological actions of all isomers of CCG were electrophysiologically examined in the isolated spinal cord of the new born rat. Eight diastereomers of CCG demonstrated a large variety of depolarizing activities. The D-CCG-II and L-CCG-IV showed potent depolarizing activity which were effectively depressed by the NMDA antagonists. The depolarization of L-CCG-I was not depressed in the presence of D-APV, CPP, and CNOX. This suggests that L-CCG-I might activate a new type of L-Glu receptors. L-CCG-III, in spite of its weak depolarizing activity, potentiated the L-Glu response. The potentiation might be due to inhibition of the L-Glu uptake process. Conformation and activity relationships between the L-isomers revealed that the NMDA receptor is activated by the folded form of Glu.
Kainoids, such as kainic acid, domoic acid, acromelic acids A and B cause marked depolarization against L-glutamate receptor in vertebrate and invertebrate. Due to their potent neuroexcitatory activity, these compounds have been used as useful tools in neuropharmacology. To find the more potent kainoids and reveal the structure-activity relationship, our efforts have been made toward following three syntheses of kainoids and related compounds. (1) Syntheses of acyclic analogues of kainoid.: In these syntheses, we achieved stereoselective syntheses of β-substituted glutamic acids from lactone 9 and lactam 18. (2) Synthesis of acromelic acid families.: We succeeded in the synthesis of acromelic acid families, which had aromatic moiety at C4, by the intramolecular Diels-Alder reaction of 28 as a key step. (3) Synthesis of kainoid.: The most rational synthesis of kainoid, that is, introduction of various substituents to a common intermediate, was achieved by the use of diaryl copper lithium reagent for the substitution reaction of trans-4-tosyloxyproline with retention of configuration. Neuroexcitatory activity of the synthetic compounds was also examined. Among the six acyclic analogues of kainoid, only the (2S,3R) isomers, which have π-electrons on the β-substituent. showed neuroexcitatory activity. In the newly synthesized kainoids, phenyl derivative 43 showed comparable activity to kainic acid. phenol derivative 32 exhibited more potent activity than acromelic acid B or domoic acid, and methoxyphenyl derivative 33 was three-to fivefold potent than acromelic acid A. and the most potent excitatory reagent known so far.
We found that neutral and cationic rhodium (I) complexes of (S,S)- or (R,R)-MOD-DIOP (1 or 2) showed very high enantio-selectivity in the catalytic asymmetric hydrogenation of α-arylidenesuccinic acid half-esters (3). The optically active α-aryl-methylsuccinic acid half-esters (4) obtained are useful inter-madiates for the synthesis of optically active lignans. Total syntheses of (+)-collinusin (7), (-)-deoxypodophyllotoxin (9), and (+)-neoisostegane (14) were achieved using asymmetric hydrogenation catalyzed by the rhodium(I) complex with (S,S)-MOD-DIOP (2) as a key reaction. Thus, the absolute configurations of natural (+)-collinusin (7) and (+)-neoisostegane (14) were determined to be (R) and (M,6R,7R), respectively. The present asymmetric hydrogenation can provide a practical method for the synthesis of various optically active lignans.
Tyrosine-derived metabolites have offered much interest for their unique structures and a variety of physiologycal activities. In connection with our synthetic studies on physiologically active natural products carrying isodi-tyrosine units, total synthesis of OF4949-III (1), and K-13 (2), along with synthetic study on vancomycin (3) have been achieved. Based on the phenolic oxidation using TTN followed by zinc reduction, an aminopeptidase B inhibitor (OF4949-III, 1) and an inhibitor of angiotensin-I converting enzyme (K-13, 2) have been successfully synthesized from the corresponding tripeptides. Interesting activities against gram positive bacteria and concepts of molecular recognition have evoked total synthesis of vancomycin. Devise to construct the isotyrosine units in this antibiotic would be discussed.
C-Aryl glycosidic bonds are characteristically embedded in several new classes of quinone antibiotics in which the sugars are directly bound to the polyarene chromophores by C-C bond. Unique structures and also the significant bioactivities, e.g., antitumor properties, stimulated growing synthetic interests to these compounds. Recently, we uncovered an efficient glycosidation reaction which utilizes a new activator of glycosyl fluoride, that is, Cp_2MCl_2-AgClO_4 (M=Zr, Hf). We envisioned to apply this new glycosyl activation to the C-aryl glycoside synthesis stated above. The results along these lines is reported herein. (1) Friedel-Crafts Approach to C-Aryl Glycosides: Coupling reaction between glycosyl fluoride and aromatics is efficiently promoted by Cp_2ZrCl_2-AgClO_4 in CH_2Cl_2 at room temperature to give C-aryl glycosides in high yield. Regioselectivity of the reaction of substituted naphthalenes are examined. (2) O→C-Rearrangement Approach to C-Aryl Glycoside: In the presence of Lewis acid, reaction between glycosyl fluoride and phenols gives rise to the O-glycoside as the initial product, which rearranges to its C-congener during gradual warming of the reaction temperature. This two-step reaction, O-glycosidation (Step 1) and O→C-rearrangement (Step 2), proceeds in one pot in the presence of Lewis acid such as BF_3・OEt_2, SnCl_4. Cp_2HfCl_2-AgClO_4 is even more effective in promoting both of the steps. This approach is particularly effective in forming the C-C bond regioselectively at the ortho-position of the phenolic hydroxyl, which is generally complementary to the outcome obtained by the Friedel-Crafts approach. (3) Synthetic Study toward Vineomycin B_2: Based on the tactics stated above, synthetic study toward vineomycin B_2 is undertaken. The reaction between D-olivosyl fluoride 10 and an anthrol derivative 20 cleanly proceeded to afford 21, which is further converted to anthraquinone 22.
The first total synthsis of pyridomycin (1) is described, in which the construction of the exocyclic (Z)-s-butylidene moiety in the 12-membered ring system of 1 was well achieved through an efficient stereocontrolled route. Following a straightforward preparation of the linear azido carboxylic acid 14 from the three subunits 4,5 and 6, the 12-membered ring compound 15 was synthesized by reduction of the azido group and DCC-HOBt cyclisation of the resulting seco-amino carboxylic acid. Dehydration and ozonolysis of 15 gave the key intermediate 3. Stereo-controlled construction of the exocyclic (Z)-s-butylidene side chain of 1 was achieved by lithium dimethylcuprate coupling to the enol phosphate of 3 under the modified Weiler's conditions. The resulting 2d was transformed into pyridomycin (1) by three-step manipuration including the introduction of the hydroxypicolinyl moiety.
Venturicidin A, B and Irumamycin, isolated from some streptomyces, are 20-membered macrolide antibiotics and inhibit effectively the growth of the phytopathogenic fungi. We have already determined the absolute structure of C_<16>-C_<22> part of irumamycin by stereoselective synthesis of the degradation product. We now report the first total synthesis of the aglycone of venturicidin A and B. Compound 14 involving four chiral centers has been synthesized in the process of determining the stereostructure of irumamycin based on the lipase-catalyzed kinetic hydrolysis and stereoselective ketone reduction and was converted to the upper half 22 in 20 steps. The bottom half 43 was prepared by regioselective dehydration of 41, which was derived from (7S)-alcohol 39. Both fragments were condensed by Yamaguchi's method to give the ester which was deprotected to give the alcohol 44. Oxidation of 44 followed by cyclization (Nicolaou's procedure) provided the 20-membered enone 45, which was reduced with NaBH_4-CeCl_3 to a separable 1:1 mixture of 46a,b. One of the isomers 46a was converted to 50a whose NMR spectrum was found to be identical with the reported spectrum of venturicidin A and B aglycone.
Bryostatin 7 (2), isolated in minute quantities from the marine organism Bugula neritina, exhibits promising antineoplastic activity. Its unique structual feature and physiological properties as well as the difficulty in its isolation from natural sources make this compound an attractive synthetic target. Our project directed toward this objective has now reached its final stage and the seco-acid corresponding to (2) is in our hands. Scheme 2 outlines a retrosynthesis of (2). Intermediate (10) was prepared through a route similar to that for fragment AB (7) (Scheme 1), while assembly of C (5) and D (6) led to CD (8) (Scheme 4). Scheme 6 outlines the coupling of A'B-CD and subsequent transformation of (21) to the seco-acid derivative (23). Thus the coupling employed the Julia-Lythgoe procedure with PhLi as a base for deprotonation of (8). The oxidation states both at the C-31 and C-35 positions was adjusted and the C-20 hydroxy group converted to the acetoxy to provide compound (22). At this stage the last asymmetric center was formed by using (12) with 3:1 stereoselection. The major (23) was isolated after selective deprotection of acetonide. The only task that remains to be achieved is macrolactonization.
The 16-membered aglycones of the largest group of macrolide antibiotics are classified into four types I, II, III and IV, according to their oxidation level. The stereoselective synthesis of I-IV by reduction and/or epoxidation on the basis of the conformational control of 16-membered rings were described. The C1-C10 (1) and C11-C15 segment (2) were coupled and cyclized by the intramolecular Wittig-Horner reaction to give a 16-membered lactone (4), which was converted to ten typical macrolide aglycones(Ia-IVc). Conformation of each-compound was controlled by changing the protection pattern of 3,5,6"-hydroxy groups. The complete stereoselective reduction and epoxidation were achieved, and the results of the diastereoselectivity of C9 carbonyl reduction and the epoxidation were clearly explained by coupled with NOE, NOESY measurement, X-ray analysis and MMP2-CONFLEX2 calculation.
Sites of action of anti-mitotic compounds to tubulin has been classed to two sites; colchicine site and vinblasitne/maytansine site. In our study on interaction between tubulin and rhizoxin, a potent spindle poison, it was suggested that rhizoxin binds to the maytansine site, the third site, different from those for colchicine and vinblastine. In our present study, we attempted modification of rhizoxin and 20-demethoxy-20-hydroxy-ansamitocin P-3 (2c, a maytansinoid compound) for the purpose of constructing the photo-affinity probe for the rhizoxin/maytansine site. Rhizoxin was converted to 20,21-seco-20-al (7) by successive OsO_4 and NaIO_4 treatments, and the aldehyde 7 was reduced with NaBH_3CN to give 20,21-seco-20-01 (8). The compounds 7 and 8 were transformed to a variety of derivatives with modified side chains, 7a-f and 8a-i respectively. Their biological activity was tested. Inhibition of tubulin polymerization by the Wittig reaction products 7a-f were as strong as rhizoxin, whereas such activity of the 20-ol-acylates 8a-i was much weaker. 20-Demethoxy-20-hydroxy-ansamitocin P-3 (2c) was converted to a vriety of 20-ol acylates 9a-f. Their inhibiton of tubulin polymerization were as potent as ansamitocin P-3. In addition, the binding of [^<14>C]20-demethoxy-20-p-azido-benzoyloxy-ansamitocin P-3 (9f) was shown to be competitive to ansamitocin P-3 (2b) and rhizoxin (1). The compound 9f was thus selected as the first photo-affinity probe for the rhizoxin/maytansine site.
Choke disease fungus Epichloe typhina is associated with resistance to leaf spot disease in timothy plants (Phleum pratense). We have proposed the hypothesis that this resistance is caused by antifungal compounds existing in infected plants. We investigated the fungitoxic constituents of the stromata of E. typhina. Seventy-eight compounds were isolated, including twenty novel sesquiterpenoids chokols (1,2,7-17,19-21,23-26), five novel oxygenated fatty acids(27-31), gamahonolide A(34) and B(37), gamahorin(38) and non-fungitoxic chokorin(71) and an anthrasteroid(80). Their structures were determined by spectroscopic methods. The absolute configuration of chokol E(2) was elucidated by its CD spectrum with Eu(fod)_3 and a chemical correlation with epicyclonerodiol oxide(5). Phytol(81), phytyl acetate(82) and phytyl palmitate(83) were identified as an inducer of aerial hyphae formation of Cladosporium herbarum. Pinoresinol(60) and diosmetin(73) were metabolized in cultures of E. typhina. Pinoresinol(60) was transformed into C6 norlignan(59) and α-ribofuranoside(87). Diosmetin(73) was transformed into 7-O-α-ribofuranoside(88). Antifungal activities of the isolated compounds were investigated.
Anatoxin-a(s) is a neurotoxic alkaloid associated with the blue-green alga Anabaena flos-aquae. Its potent toxicity (LD_<50> 20-40μg/kg mice) is attributed to exceptional anticholinesterase activity. Acidic alcoholic extract of the freeze-dried alga was subjected to patitioning and extraction with acidic alcoholic solutions to give a toxic concentrate. Gel filtration on Toyopearl HW40F (Supelco) followed by HPLC on CN and ODS columns gave pure anatoxin a(s) as a colorless solid in 0.05% yield. The gross structure of anatoxin a(s) was determined by spectroscopic method on the toxin itself and on the degradation products. NMR data of the ^<13>C and ^<15>N enriched toxin were indispensable for the work. The absolute configuration of anatoxin a(s) was elucidated by synthesizing one of the degradation products from L-Asn.
Emericella heterothallica is a typical heterothallic fungus. From the mycelial extract of E. heterothallica, strain ATCC 16847 (mating type A), novel epidithiodioxopiperazines, emethallicin A (1) as the major metabolite, and emethallicins E (5) and F (6) as the minor components, were isolated along with ergosterol. On the other hand, novel epitetrathiodioxopiperazines, emethallicins B (2) and C (3), and an epitrithiodioxopiperazine, emethallicin D (4), were isolated from the mycelial extract of E. heterothallica, strain ATCC 16824 (mating type a). The structures of 1-6 were determined on the basis of the spectroscopic and chemical investigation of themselves and their derivatives. It is interesting that dibenzyldioxopiperazine derivatives (13-18) were also isolated from the extract of the culture filtrate of the above two strains. Emethallicins A-F (1-6) have the same basic skeleton as apoaranotin (9), aranotin (12), or their related novel basic skeleton. Emethallicins are the first exaples of isolation of mandelic acid, as a free acid and/or its ester, from fungi. Emethallicins A-F (1-6) have the potent inhibitory activity against compound 48/80-induced histamine release from mast cells, and are also 5-lipoxygenase inhibitors.
The circadian clock is considered to be a univerasal feature of eucaryotic organisms, controlling the occurrence and rates of many different aspects of life, ranging from single enzymatic reactions and metabolism to complex behaviours such as activity and rest. Although the nature of the underlying cellular/biochemical oscillator is still unknown, many substances such as inhibitors of protein synthesis and D_2O are known to influence either phase or period of circadian rhythms in differnt organisms. We have found that the period of free-running circadian rhythms in the unicellular marine alga Gonyauloax polyedra is shortened by extracts from several organisms including bovine brain and muscle and Gonyaulax polyedra itself. The effect is dose dependent, accelerating the circadian clock up to 4 hours per day. The exogenous period-shortening substance has been isolated from bovine muscle and identified as creatine. The endogenous period-shortening substance, gonyaulin, has been obtained from Gonyaulax itself and the structure has been determined to be 1 on the basis of the spectroscopic data and confirmed by total synthesis from 4.
Biosynthesis of the optically active Diels-Alder type adducts in the mulberry tree (Moraceae) has been examined by the administration of O-methylated precursory chalcones to Morus alba cell cultures. From the cell cultures incubated with 2,2',4'-trihydroxy-4-methoxychalcone (3), 3'-prenylated 3 (4), 4-O-methyl-kuwanon J (5), 4-O-methyl-kuwanon Q (6), 4,18"-di-O-methyl-kuwanon J (7), and 18"-O-methyl-chalcomoracin (8) were obtained. Furthermore, 12",16",18"-tri-O-methyl-chalcomoracin (11) was isolated from the cell cultures incubated with 2'-hydroxy-2,4,4'-trimethoxy-3'-prenylchalcone (10). These O-methylated Diels-Alder type adducts 5, 6, 7, 8, and 11 were optically active, and the patterns of their CD spectra were in good agreement with those of chalcomoracin (1) and kuwanon J (2). These results indicated that the O-methylchalcones 3 and 10 are incorporated into the biosynthetic pathway resulting in the formation of optically active adducts through a Diels-Alder type cycloaddition reaction of the α,β-double bond of the chalcone as a dienophile with the prenyl portion as a diene.
The biosynthesis of isoflavonoids was investigated at the enzyme level with elicitor-treated cell suspension cultures of Pueraria Iobata Ohwi (Leguminosae). Our interests were focused mainly on two enzymatic reactions catalyzed by isoflavone synthase (IS) and deoxychalcone synthase (DOCS). IS catalizes the 1,2-aryl migration of B ring, and DOCS achieves the condensation and the reduction during the construction of aromatic A ring. The deoxy type flavanone(2a) and chalcone(1a) were both converted into the corresponding isoflavone(3a) by a microsomal preparation containing chalcone-flavanone isomerase. Competitive experiments with [^3H]flavanone and [^<14>C]chalcone revealed that flavanone is the true substrate of IS. IS reaction required NADPH and O_2 and was inhibited by CO gas or SKF525A. These observations suggest that IS is an enzyme belonging to P-450. DOCS system in P. lobata was partially purified and revealed to be composed of two separate enzymes, chalcone synthase and coacting reductase. DOCS is a new type of polyketide synthase which affords a deoxy-type compound in the presence of NADPH and a hydroxy-type compound in the absence of NADPH.
Limonene synthase responsible for the cyclization of geranyl diphosphate (GPP) to limonene was partially purified from the leaves of Mentha spicata and Citrus unshiu. Divalent metal cations, especially Mg^<2+>, binds to the diphosphate moiety of GPP in a mole ratio of 1:1 in the initial stages of the biosynthesis of cyclic monoterpenoids. The chelation weakens the C-O bond of these diphosphates to facilitate the elimination of the diphosphate group, and this results in the formation of allylic cation as an intermediate in the cyclization of GPP. Incubation of geranyl diphosphate (GPP) with the limonene synthase gave (S)-(-)-limonene in case of the enzyme isolated from M. spicata and (R)-(+)-limonene in case of the enzyme isolated from C. unshiu. On the other hand, incubation of enantiomers of linalyl diphosphate (LPP) with the limonene synthase resulted in the conversion of (S)-LPP into (S)-limonene in the case of the enzyme from M. spicata and (R)-LPP into (R)-limonene in the case of the enzyme from C. unshiu. These facts clearly indicate that allylic cations with the configuration similar to (S)- and (R)-LPP are involved as intermediates in the cyclization of GPP to (S)- and (R)-limonene, respectively. Thus, the process for the cyclization of the C_<10>-prenyl chain is probably as follows: GPP bound to the active sites of limonene synthase is transformed into the stereochemically specified allylic cation [(a) or (e) in Fig. 3] under the steric control characteristic of the enzyme in the respective plants and then the allylic cation is led to the formation of the stereospecifically featured cyclic monoterpenoids.
More than fifty compounds of medium sized haloether having a straight C_<15>-chained skeleton and terminal enyne or bromoallene moieties were isolated from marine origins such as red algae, Laurencia species and sea hare, Aplysia species. The presumed precursors of these haloethers, laurediols (13 and 14) have been isolated from L. nipponica. However, biosynthetic studies have not been attempted since its isolation in 1972. We wish to report herein that partially saturated laurediol mimics (15 and 16) have been cyclized by commercially available lactoperoxidase, hydrogen peroxide, and bromide ion to give bromooxolanes (17, 18, and 19) and bromohydrins. When unsaturated diol, (6S,7R,12E)-12-penta-decen-6,7-diol was subjected to the same enzymatic reaction, eight membered bromoether, octahydrodeacetyllaurencin (20) was obtained in 1% yield. These results strongly suggested that laurediols are real precursors of haloethers. Furthermore, deacetyllaurencin (2) was converted by the same enzymatic reaction into laurefucin (3) and laureoxanyne (22). This indicates that deacetyllaurefucin was also the biosynthetic key intermediate for bicyclic bromoethers. Finally, natural bromoperoxidase prepared from L. nipponica was applied to the reactions and the same results were observed with the low yield. Consequently, we could conclude that bromoperoxidase is the actual enzyme for bromo-etherification in vivo and bromo-cationic reaction causes bromine incorporation into the organic compounds in the alga.
Teleocidins produced by actinomycetes are potent tumor promoters and peculiar indole alkaloids containing a nine-membered lactam ring and a complex monoterpenoid moiety. Among the teleocidin-producing actinomycetes, Streptoverticillium blastmyceticum NA34-17, which we had found to produce the Epstein-Barr virus early antigen inducing indole alkaloids, has a characteristic feature of producing (-)-indolactam V (1), the common biosynthetic intermediate of teleocidins, in quantity. This characteristic would be advantageous to obtain a wide variety of biosynthetic intermediates of teleocidins. Using this microorganism, the possible biosynthetic pathway of teleocidins shown in Fig. 8 was proposed by feeding experiments with several D or ^<13>C-labelled precursors and isolation of new teleocidin-related metabolites named blastmycetin D (8) and E (9). Feeding experiments with several D or ^<13>C-labelled amino acids and possible biosynthetic precursor showed that (-)-indolactam V (1) was biosynthesized from L-tryptophan, L-valine and L-methionine via N-methyl-L-valyl-L-tryptophanol (3). From the isolation of blastmycetin D (8) and E (9), and feeding experiments with D-labelled L-methionine, we proposed the hypothesis that (-)-N^1-nerylindolactam V was a common biosynthetic intermediate of teleocidins, and that the complex monoterpenoid moieties of teleocidins, for example those of olivoretin A, C and E (see Fig. 8), arose by difference of the sequence of the methylation and the aza-Claisen rearrangement, and the position of the methylation.
In order to overcome some problems with 2D NMR, we have developed three NMR techniques, time sharing decoupling NOE (TSD-NOE), selective HOHAHA-CH and selective HOHAHA-COSY. TSD-NOE, which utilizes composite 90 degree pulse for observation and time sharing decoupling, enables to carry out 1D NOE experiments with extremely high selectivity. Selective HOHAHA-CH detects proton magnetization transferred from a specific proton by carbon-13 and is a very good technique to analyze congested methylene proton regions. Selective HOHAHA-COSY is a combination of HOHAHA and COSY and very powerful for analyzing complicated proton spin systems. These techniques has been applied for structural elucidation of a new antibiotic SS49 (C_<40>H_<68>O_<11>). SS49 is structurally related to cytovaricin and phthoramycin as shown in Fig. 11.
Six new stable anthocyanins, named ternatin A1, A2, B1, B2, D1 and D2, were isolated from the blue flowers of Clitoria ternatea L.. The structures of two common components prepared from alkaline deacylation of ternatin mixture were determined as E-4-p-coumaryl β-D-glucoside(1) and delphinidin 3,3',5'-tri-β-D-glucoside(2), respectively. Based on the HPLC analysis of deacylated products and FAB-MS data, the structure of each ternatin was estimated. Thus the structures of ternatin D1, A1 and A2 were completely identified as 3, 4 and 5 by PMR, CMR and DIFNOE spectroscopies. The 3',5'-side chains of 3 and 4 had high symmetry forms more than that of 5. The exceptional color stability of ternatins in a neutral solution is attributed to the intramolecular copigmentation(stacking) between delphinidin nucleus and p-coumaryl moieties of 3',5'-side chains.
In search of new bioactive substances from marine organisms, we have investigated the chemical constituent of an Okinawan marine sponge Xestosponqia sp. and isolated eight new alkaloids named araguspongines B (8), C (9), D (1), E (7), F (3), G (2), H (5), and J (4) which were characterized by having two 1-oxaquinolizidine moieties. By HPLC analysis using a chiral column, these alkaloids were divided into two classes: the one obtained as a single enantiomer [F (3), G (2), H (5), J (4)] and the other as an enantiomeric mixture [B (8), D (1), E (7)]. In the further study, we isolated a new alkaloid named aragupetrosine A (18) (single enantiomer) together with two knowns, petrosin (11)(an enantiomeric mixt.) and petrosin A (15)(mesomeric), which were characterized by having two 2-oxoquinolizidine moieties. Aragupetrosine A (18) is a hybrid of petrosin (11) and araguspongine F (3). The fact, that araguspongines F (3), G (2), H (5), J (4), and aragupetrosine A (18) were respectively obtained as a single enantiomer while others as enantiomeric mixtures or as a mesomeric compound, may be explained by presuming enantio-selective methylation to occur at C-3 prior to (or after) formation of the racemic 1-oxaquinolizidine moieties. These alkaloids showed stronger vasodilative activities than papaverine in the perfusion model experiment using an isolated mesenteric artery of SD-rat.