Synthesis and antitumor activity of 7-O-[2,6-dideoxy-2-fluoro-5-C-(trifluoromethyl)-alpha-L-talopyranosyl]- daunomycinone and -adriamycinone.

7-O-[2,6-Dideoxy-2-fluoro-5-C-(trifluoromethyl)-alpha-L-talopyranosyl]- daunomycinone and -adriamycinone have been prepared by the coupling of 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-5-C-(trifluoromethyl)-alpha-L- talopyranosyl iodide with daunomycinone. The key steps in this synthesis are the regioselective fluorination of methyl alpha-D-lyxopyranoside to give the 4-deoxy-4-fluoro-beta-L-ribopyranoside and the C-trifluoromethylation of the aldehydo-L-ribose derivative to give the 1,1,1-trifluoro-5-monofluoro-L-altritol derivative. Antitumor activities of the synthetic products were compared with those for the 2'-deoxy-2'-fluoro and 2',6'-dideoxy-5'-C-trifluoromethyl analogs.     

Anthracycline glycosides of 2,6-dideoxy-2-fluoro-alpha-L-talopyranose

The methyl beta-glycoside of the title sugar, obtained from 2-deoxy-2-fluoro-beta-D-glucopyranose tetraacetate by a sequence with detailed characterization of all intermediates, was converted by acetolysis-bromination into 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-alpha-L-talopyranosyl bromide, coupling of which with (7S,9S)-4-demethoxydaunomycinone afforded the 3,4-diacetate of 4-demethoxy-9-O-(2,6-dideoxy-2-fluoro-alpha-L-talopyranosyl)daunomycinone (19). The antitumor-active 19 was converted by way of its 14-bromo derivative into the 14-hydroxy analogue, the antitumor-active 4-demethoxyadriamycinone glycoside 21.     

Microbial transformation of semisynthetic derivatives of daunomycinone modified in ring a

Semisynthetic derivatives of daunomycinone with 7,9-isopropylacetal, 7-O-methyl, 7-O-(4-penten-2-yl), and 7-O-(2-hydroxyethyl) substituents were converted byStreptomyces peucetius var.caesius (an adriamycin-blocked mutant) into 7-deoxy-13-dihydrodaunomycinone, while daunomycinone was transformed into 13-dihydrodaunomycinone (predominantly) and 7-deoxy-13-dihydrodaunomycinone.S. coeruleorubidus mutants 24–74 (accumulating aclavinone derivatives instead of daunomycin and related compounds) and 96-85 (producing no anthracycline substances), andS. aureofaciens B-96 (a tetracycline-blocked mutant) transformed the above substrates into the corresponding 13-dihydro derivatives, with the exception of 7,9-isopropylacetal daunomycinone which remained intact. 7-O-Propyn-1-yl daunomycinone was not transformed by any of the strains used under the conditions.     

Concise syntheses of arabinogalactans with beta-(1-->6)-linked galactopyranose backbones and alpha-(1-->3)- and alpha-(1-->2)-linked arabinofuranose side chains

4-methoxyphenyl glycosides of 2,3'-bis-alpha-L-arabinofuranosyl branched beta-D-(1-->6)-linked galactopyranosyl tetraose (16), 3',2'-bis-alpha-L-arabinofuranosyl branched beta-D-(1-->6)-linked galactopyranosyl hexaose (27), and a twentyose (42) consisting of beta-(1-->6)-linked D-galactopyranosyl pentadecaoligosaccharide backbone with alpha-L-arabinofuranosyl side chains alternately attached at C-2 and C-3 of the middle galactose residue of each consecutive beta-(1-->6)-linked galactotriose unit of the backbone, were synthesized with isopropyl 3-O-allyl-2,4-di-O-benzoyl-1-thio-beta-D-galactopyranoside (6), 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (7), 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl trichloroacetimidate (12), 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (17), 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranoside (19), and 2,6-di-O-acetyl-3,4-di-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (28) as the key synthons. Condensation of 6 with 7 gave the disaccharide donor 8, and subsequent condensation of 8 with 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranosyl-(1-->6)-2-O-acetyl-3,4-di-O-benzoyl-beta-D-galactopyranoside (9) followed by selective deacetylation afforded the tetrasaccharide acceptor 11. Coupling of 11 with 12 gave the pentasaccharide 13, its deallylation followed by coupling with 12, and debenzoylation gave the hexasaccharide 16 with beta-(1-->6)-linked galactopyranose backbone and 2- and 3'-linked alpha-L-arabinofuranose side chains. The octasaccharide 27 was similarly synthesized, while the twentyoside 42 was synthesized with tetrasaccharides 33 or 24 as the donors and 23, 36, 38, and 40 as the acceptors by consecutive couplings followed by deacylation.     

Synthesis and biological activity of 2'-deoxy-4'-thio-pyrazolo[3,4-d]pyrimidine nucleosides

The coupling of 4-aminopyrazolo [3, 4-d]pyrimidine with the appropriate thio sugar gave a 3:1 ratio of alpha,beta blocked 4-amino-1-(2-deoxy-4-thio-D-erythropentofuranosyl)-1H pyrazolo[3,4-d]pyrimidine nucleosides. The mixture was deblocked, both the anomers were separated, and the beta-anomer was readily deaminated by adenosine deaminase. The nucleosides have been characterized, and their anomeric configurations have been determined by proton NMR. All three nucleosides were evaluated against a panel of human tumor cell lines for cytotoxicity in vitro. The details of a convenient and high yielding synthesis of these nucleosides are described.     

The synthesis of 5-C-(6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranos-6-yl)-2 ,3-O-isopropylidene-D-allo-pentofuranose [deaminotri-O-isopropylidene tunicamine]

Three approaches to the synthesis of deaminotunicamine and derivatives were developed. Tin tetrachloride condensation of 6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galacto-heptodialdo-1, 5-pyranose with 2-(trimethylsilyloxy)furan gave a mixture of stereoisomeric precursors. Condensation of 1,2:3,4-di-O-isopropylidene-alpha-D-galacto-hexodialdo-1,5-pyranos e with the phosphate carbanion obtained from diethyl (2-furyl)methoxymethyl phosphonate led to 6-deoxy-7-C-(2-furyl)-1,2:3,4-di-O-isopropylidene-L-glycero-alpha-D- galactoheptopyranose (13). This was converted, via the "delta 2"-butenolide route, to a mixture of stereoisomeric 5-C-(6-deoxy-alpha-D-galactopyranos-6-yl)-pentono-1,4-lacton es of the D-allo and D-talo configuration. In the third approach, 13 was transformed by the "enulose" approach to deamino-tri-(O-isopropylidene)tunicamine.     

Synthesis and antitumor activity of 3'-C-methyl-daunorubicin

Reaction of 1,5-anhydro-4-O-benzoyl-2,3,6-trideoxy-3-C-methyl-3-trifluoro-acetami no-L-lyxo-hex-1-enitol with daunomycinone in the presence of anhydrous toluene-p-sulfonic acid in benzene, followed by removal of the N- and O-protecting groups under mild conditions, gave 3'-C-methyldaunorubicin. The antitumor activity of the new anthracycline glycoside has been evaluated.     

Biotransformations of anthracyclinones inStreptomyces coeruleorubidus andStreptomyces galilaeus

The ability to transorm biologically exogenous daunomycinone, 13-dihydrodaunomycinone, aklavinone, 7-deoxyaklavinone, epsilon-rhodomycinone, epsilon-isorhodomycinone and epsilon-pyrromycinone was studied in submerged cultures of the following strains: wild Streptomyces coeruleorubidus JA 10092 (W1) and its improved variants 39-146 and 84-17 (type P1) producing glycosides of daunomycinone and of 13-dihydrodaunomycinone, together with epsilon-rhodomycinone, 13-dihydrodaunomycinone and 7-deoxy-13-dihydrodaunomycinone; in five mutant types of S. coeruleorubidus (A, B, C, D, E) blocked in the biosynthesis of glycosides and differing in the production of free anthracyclinones; in the wild Streptomyces galilaeus JA 3043 (W2) and its improved variant G-167 (P2) producing glycosides of epsilon-pyrromycinone and of aklavinone together with 7-deoxy and bisanhydro derivatives of both aglycones; in two mutant types S. galilaeus (F and G) blocked in biosynthesis of glycosides and differing in the occurrence of anthracyclinones. The following bioconversions were observed: daunomycinone leads to 13-dihydrodaunomycinone and 7-deoxy-13-dihydrodaunomycinone (all strains); 13-dihydrodaunomycinone leads to 7-deoxy-13-dihydrodaunomycinone (all strains); daunomycinone or 13-dihydrodaunomycinone leads to glycosides of daunomycinone and of 13-dihydrodaunomycinone, identical with metabolites W1 and P1 (type A), or only a single glycoside of daunomycinone (type E); aklavinone leads to epsilon-rhodomycinone (types A and B); aklaviinone leads to 7-deoxyaklavinone and bisanhydroaklavinone (type C); epsilon-rhodomycinone leads to zeta-rhodomycinone (types C, E); epsilon-rhodomycinone leads to glycosides of epsilon-rhodomycinone (types W2, P2); epsilon-isorhodomycinone leads to glycosides of epsilon-isorhodomycinone (types W2, P2); epsilon-pyrromycinone leads to a glycoside of epsilon-pyrromycinone (types W1, P1). 7-Deoxyaklavinone remained intact in all tests. Exogenous daunomycinone suppressed the biosynthesis of its own glycosides in W1 and P1; it simultaneously increased the production of epsilon-rhodomycinone in P1.     

SYNTHESIS AND BIOLOGICAL ACTIVITY OF 2′-DEOXY-4′-THIO-PYRAZOLO[3,4-d]PYRIMIDINE NUCLEOSIDES

The coupling of 4-aminopyrazolo [3, 4-d]pyrimidine with the appropriate thio sugar gave a 3:1 ratio of α,β blocked 4-amino-1-(2-deoxy-4-thio-D-erythropentofuranosyl)- 1H pyrazolo[3,4-d]pyrimidine nucleosides. The mixture was deblocked, both the anomers were separated, and the β-anomer was readily deaminated by adenosine deaminase. The nucleosides have been characterized, and their anomeric configurations have been determined by proton NMR. All three nucleosides were evaluated against a panel of human tumor cell lines for cytotoxicity in vitro. The details of a convenient and high yielding synthesis of these nucleosides are described.     

Synthesis of an alpha-linked dimer of the trisaccharide repeating unit of the exopolysaccharide produced by Pediococcus damnosus 2.6

A hexasaccharide, beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->2)]-alpha-D-Glcp-(1-->3)-beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->2)]-D-Glcp, the alpha-linked dimer of the trisaccharide repeating unit of the exopolysaccharide produced by Pediococcus damnosus 2.6, was synthesized as its methyl glycoside. Condensation of fully benzoylated alpha-D-glucopyranosyl trichloroacetimidate (1) with isopropyl 4,6-O-benzylidene-1-thio-beta-D-glucopyranoside (2) selectively furnished (1-->3)-linked disaccharide 3, and subsequent 2-O-acetylation, desulfation, and trichloroacetimidate formation afforded the disaccharide donor 6. Meanwhile, selective 3-O-coupling of methyl 4,6-O-benzylidene-alpha-d-glucopyranoside (8) with 3-O-allyl-2,4,6-tri-O-benzoyl-alpha-D-glucopyranosyl trichloroacetimidate (7), followed by coupling with 1 gave the trisaccharide 10. Removal of the benzylidene group of 10, benzoylation, and deallylation produced the trisaccharide acceptor 12. Condensation of 12 with 6 yielded a pentasaccharide mixture 13 with beta and alpha isomers in a ratio of 2:1. Removal of the benzylidene group of 13, followed by benzoylation gave the pentasaccharide mixture 14. Selective 2'-deacetylation of the isolated beta-linked 14beta with MeCOCl/MeOH/CH2Cl2 did not give the expected pentasaccharide acceptor, and serious decomposition occurred, indicating a large steric hindrance at C-2'. Alternatively, 2,3-di-O-glycosylation of allyl 4,6-O-benzylidene-beta-D-glucopyranoside (21) with 1 gave 22, then deallylation and trichloroacetimidate formation afforded the trisaccharide donor 24. Condensation of 12 with 24 furnished only the alpha-linked hexasaccharide 25, and its deprotection gave the free hexaoside 27.     

Stereoselective reactions of (20R)-3,20-dihydroxy-(3',4'-dihydro-2'H-pyranyl)-5-pregnene derivatives form 27-nor-3,20,23,26-tetrahydroxy-cholesten-22-ones and related bromo ketones

The previously reported analog of pregnenolone having a 3,4-dihydro-2H-pyran attached via a Cz.sbnd;C bond to the C-20 position (1), stereoselectively reacts with m-chloroperoxybenzoic acid in methanol at -5 degrees C. Acid-catalyzed hydrolysis of the isolated intermediates gives good yields of mostly a new 27-norcholesterol analog: (20R,23R)-3,20,23,26-tetrahydroxy-27-norcholest-5-en-22-one-3-acetate (2a, and a smaller amount of its 23S enantiomer 2b). Three different conditions of epoxidation and methanolysis followed by acid-catalyzed hydrolysis typically produce approximately 2:1 ratios of the 23R:23S diastereoisomers with a C-23 hydroxy group at the new asymmetric center. Bromine also reacts stereoselectively with (20R)-3,20-dihydroxy-(3',4'-dihydro-2'H-pyranyl)-5-pregnene (4) giving mostly (20R,23R)-23-bromo-3,20,26-trihydroxy-27-norcholest-5-en-22-one (7a). Thus both major steroidal products 2a and 7a have the same C-23R configuration. Assignment of molecular structures and the absolute configurations to 1 and 2a were based on elemental analysis, mass spectra, nuclear magnetic resonance, FTIR infrared spectroscopic analysis and X-ray crystallography. Mechanisms are discussed for stereochemical selectivity during epoxidation and bromination of the 3,4-dihydro-2H-pyranyl ring in 1 and 4.     

An N2S2 bifunctional chelator for technetium-99m and rhenium: complexation, conjugation, and epimerization to a single isomer.

A bifunctional chelator 6 was prepared bearing an N2S2 core for binding rhenium or technetium and a carboxylic acid group for conjugation to amino groups of biomolecules. Complexation of 6 with rhenium(V) resulted in two kinetic isomers, anti-7 and syn-7, being formed in approximately equal amounts. Epimerization with 0.5 M NaOH yields a single isomer anti-7, as determined by NMR spectroscopy and single-crystal X-ray analysis. The 99mTc complex was prepared at the tracer level by reaction of the ligand with 99mTcO4-, tin(II) chloride and sodium gluconate giving a mixture of two isomers, but showing a preference for the anti isomer. Chelation in the presence of 1 M NaOH results in anti-8 being formed as the sole product. The bifunctional ability of the ligand was explored by amide formation with (S)-alpha-phenethylamine, either by direct DCC coupling or through the N-hydroxy succinimidyl ester 9 intermediate. The deprotected bioconjugate 11 was complexed with rhenium, yielding similar amounts of two isomeric rhenium complexes, anti-12 and syn-12, which were isolated and characterized by NMR spectroscopy. Treatment of the kinetic mixture of anti-12 and syn-12 with 1 M NaOH resulted in quantitative conversion to a single rhenium complex anti-12. With technetium-99m in 0.1 M sodium acetate, bioconjugate 11 yielded both technetium-99m complexes anti-13 and syn-13, in a 2:1 ratio, respectively. In contrast, complexation in the presence of 1 M NaOH gave only one technetium-99m complex, assigned the structure anti-13.     

An efficient and practical synthesis of beta-(1 --> 3)-linked xylooligosaccharides

A facile and practical method was developed for the synthesis of beta-(1 --> 3)-linked xylooligosaccharides. Dibezoylation of allyl alpha-D-xylopyranoside (1) afforded 2,4-dibenzoate 6 as the major product. Chloroacetylation of 6, followed by deallylation and trichloroacetimidation, gave a 1:3 alpha/beta imidate (10 and 11) mixture. Coupling of the imidate mixture with 6 gave a disaccharide 13, whose dechloroacetylation afforded the disaccharide acceptor 16. Condensation of perbenzoylated xylosyl alpha/beta imidate (7 and 8) mixture with 6 gave the disaccharide 12. Deallylation of 12, followed by trichloroacetimidation, furnished the disaccharide donor as a 1:1 alpha/beta mixture. Coupling of the disaccharide donor mixture with the disaccharide acceptor 16 yielded the tetrasaccharide 17. Reiteration of deallylation and trichloroacetimidation transformed 17 to the tetrasaccharide donor mixture. Condensation of the tetrasaccharide donor mixture with the acceptor 16 gave the hexasaccharide 21. Debenzoylation with saturated ammonia-methanol afforded beta-(1 --> 3)-linked allyl xylotetraoside and xylohexaoside.     

A concise synthesis of two isomeric pentasaccharides, the O repeat units from the lipopolysaccharides of P. syringae pv. porri NCPPB 3364T and NCPPB 3365

A concise synthesis of two isomeric pentasaccharides, alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->3)-[beta-D-GlcpNAc-(1-->2)]-alpha-L-Rhap (A) and alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1-->3)-[beta-D-GlcpNAc-(1-->2)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap (B), the O repeats from the lipopolysaccharides of Pseudonomonas syringae pv. porri NCPPB 3364T and 3365 was achieved via assembly of the building blocks, allyl 3,4-di-O-benzoyl-alpha-L-rhamnopyranoside (1), 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (2), allyl 4-O-benzoyl-3-O-chloroacetyl-alpha-L-rhamnopyranoside (6), 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate (7), and allyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside (10). Coupling of 1 with 2 followed by deallylation and trichloroacetimidate formation gave the disaccharide donor 5, while condensation of 6 with 7, followed by dechloroacetylation, offered the disaccharide acceptor 9. Then, 5 was coupled with 10 to obtain the trisaccharide 11, and subsequent deallylation and trichloroacetimidate formation furnished the trisaccharide donor 13. Coupling of 9 with 13, followed by deprotection, afforded pentasaccharide 19, while condensation of 9 with 5, followed by deallylation and trichloroacetimidate formation, gave the tetrasaccharide donor 16, whose coupling with 10 and subsequent deprotection yielded another pentasaccharide 22.     

Synthesis of polydeoxygenated and iodinated disaccharides.]

3-Amino-polydeoxy disaccharides have been prepared by condensation of a glycal with methyl 2,3,6-trideoxy-alpha-L-erythro-(or threo)-hex-2-enopyranoside in the presence of N-iodosuccinimide. After acid hydrolysis of the glycoside, 1,4-addition of hydrazoic acid to the corresponding hex-2-enopyranose led to 3-azido-disaccharides which were acetylated. Reduction of the azido group gave 2,2'-dideoxy- or 2,2'-dideoxy-2'-iodo compounds. Condensation of O-(3,4-di-O-acetyl-2,6-dideoxy-2-iodo-alpha-L-manno-hexopy-rano syl)-(1----4)-1- O-acetyl-2,3,6-trideoxy-3-trifluoroacetamido-alpha-L-arabino-he xopyranose with daunomycinone, followed by 3',4'-O-deacetylation produced the new anthracycline, 7-O-[O-(2,6-dideoxy-2-iodo-alpha-L-manno-hexopyranosyl)-(1----4)-2,3,6- trideoxy-3-trifluoroacetamido-alpha-L-arabino-hexopyranosyl]-da uno-mycinone.     

Synthetic mucin fragments: methyl 3-O-(2-acetamido-2-deoxy-beta-D-galactopyranosyl-beta-D- 3-O-(2-acetamido-2-deoxy-3-O-beta-D-galactopyranosyl- beta-D-glucopyranosyl)-beta-D-galactoyranoside. pyranosyl)-beta-D-galactopyranoside

Methyl 2,4,6-tri-O-benzyl-beta-D-galactopyranoside (5) was obtained crystalline by way of its 3-O-allyl derivative, which was in turn obtained by ring-opening of a presumed 3,4-O-stannylene derivative of methyl beta-D-galactopyranoside, followed by benzylation. Condensation of 5 with 2-methyl-(2-acetamido-3,4,6-tri-O-acetyl-1,2-dideoxy-beta-D-glucopyra no)-[2,1-d]-2-oxazoline in 1,2-dichloroethane in the presence of p-toluenesulfonic acid afforded the disaccharide derivative methyl 3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-2, 4,6-tri-O-benzyl-beta-D-galactopyranoside (6) Deacetylation of 6 in methanolic sodium methoxide afforded the disaccharide derivative 7, which was acetalated with alpha, alpha-dimethoxytoluene to afford the 4',6'-O-benzylidene acetal (10). Catalytic hydrogenolysis of the benzyl groups of 7 afforded the title disaccharide 8. Glycosylation of 10 with 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in 1:1 benzene-nitromethane in the presence of mercuric cyanide gave the fully protected trisaccharide derivative 12. Systematic removal of the protecting groups of 12 then furnished the title trisaccharide 14. The structures of 5, 8, and 14 were all confirmed by 13C-n.m.r. spectroscopy. The 13C-n.m.r. chemical shifts for methyl alpha- and beta-D-galactopyranoside, and also those of their 3-O-allyl derivatives, are recorded, for the sake of comparison, in conjunction with those of compound 5.     

Synthesis of p-nitrophenyl 2-O-α- and -β-l-fucopyranosyl-β-d-fucopyranoside

Reaction of 2,3,4-tri-O-acetyl-α-l-fucopyranosyl bromide with p-nitrophenyl 3,4-O-isopropylidene-β-d-fucopyranoside in the presence of mercuric cyanide in acetonitrile, followed by removal of the isopropylidene group under mild conditions, gave a mixture of p-nitrophenyl 2-O-(2,3,4-tri-O-acetyl-α- and -β-l-fucopyranosyl)-β-d-fucopyranoside. These compounds were conveniently separated by preparative, thin-layer chromatography, and, on deacetylation, gave the title disaccharides, whose structures were established by ¹H- and ¹³C-n.m.r. spectroscopy.     

Synthesis of four diastereoisomers at carbons 24 and 25 of 3 alpha,7 alpha,12 alpha,24-tetrahydroxy-5 beta-cholestan-26-oic acid, intermediates of bile acid biosynthesis

The synthesis of four stereoisomers at C-24 and C-25 of 3 alpha,7 alpha,12 alpha,24-tetrahydroxy-5 beta-cholestan-26-oic acid is described. Pyridium chlorochromate oxidation of 3 alpha,7 alpha,12 alpha-triacetoxy-5 beta-cholan-24-ol (II) prepared from cholic acid (I) afforded 3 alpha,7 alpha,12 alpha-triacetoxy-5 beta-cholan-24-al (III) which was converted to a mixture of the four stereoisomers (IV-VII) by a Reformatsky reaction with ethyl DL-alpha-bromopropionate followed by alkaline hydrolysis. Separation of these isomers (IV-VII) was achieved by silica gel column chromatography, and subsequent reversed-phase partition column chromatography. The configurations at C-24 were elucidated by conversion of each isomer into (24R)- or (24S)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24-tetrol (XII or XI) by Kolbe electric coupling, the C-24 configurations of which were determined by modified Horeau's method and 13C-nuclear magnetic resonance spectroscopy. The stereochemistries at C-25 were deduced by comparison of IV-VII with the products of the hydroboration followed by oxidation with alkaline hydrogen peroxide of (24E)-3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholest-24-en-26-oic acid (XIII).     

Synthesis of 4-substituted phenyl 2,5-anhydro-1,6-dithio-alpha-D-gluco- and -alpha-L-guloseptanosides possessing antithrombotic activity

Two independent approaches were investigated for the synthesis of 3,4-di-O-acetyl-1,6:2,5-dianhydro-1-thio-D-glucitol (18), a key intermediate in the synthesis of 1,3,4-tri-O-acetyl-2,5-anhydro-6-thio-alpha-D-glucoseptanose (13), needed as glycosyl donor. In the first approach 1,6-dibromo-1,6-dideoxy-D-mannitol was used as starting material and was converted via 2,5-anhydro-1,6-dibromo-1,6-dideoxy-4-O-methanesulfonyl-3-O-tetrahydropy ranyl-D-glucitol into 18. The second approach started from 1,2:5,6-di-O-isopropylidene-D-mannitol and the allyl, 4-methoxybenzyl as well as the methoxyethoxymethyl groups were used, respectively, for the protection of the 3,4-OH groups. The resulting intermediates were converted via their 1,2:5,6-dianhydro derivatives into the corresponding 3,4-O-protected 2,5-anhydro-6-bromo-6-deoxy-D-glucitol derivatives. The 1,6-thioanhydro bridge was introduced into these compounds by exchanging the bromine with thioacetate, activating OH-1 by mesylation and treating these esters with sodium methoxide. Among these approaches, the 4-methoxybenzyl protection proved to be the most suitable for a large scale preparation of 18. Pummerer rearrangement of the sulfoxide, obtained via oxidation of 18 gave a 1:9 mixture of 1,3,4-tri-O-acetyl-2,5-anhydro-6-thio-alpha-L-gulo- (12) and -D-glucoseptanose 13. When 12 or 13 were used as donors and trimethylsilyl triflate as promoter for the glycosylation of 4-cyanobenzenethiol, a mixture of 4-cyanophenyl 3,4-di-O-acetyl-2,5-anhydro-1,6-dithio-alpha-L-gulo- (58) and -alpha-D-glucoseptanoside (61) was formed suggesting an isomerisation of the heteroallylic system of the intermediate. A similar mixture of 58 and 61 resulted when 18 was treated with N-chloro succinimide and the mixture of chlorides was used in the presence of zinc oxide for the condensation with 4-cyanobenzenethiol. When 4-nitrobenzenethiol was applied as aglycon and boron trifluoride etherate as promoter, a mixture of 4-nitrophenyl 3,4-di-O-acetyl-2,5-anhydro-1,6-dithio-alpha-L-gulo- (60) and -alpha-D-glucoseptanoside (62) was obtained. Deacetylation of 58, 61 and 62 according to Zemplen afforded 4-cyanophenyl 2,5-anhydro-1,6-dithio-alpha-L-glucoseptanoside (59), 4-cyanophenyl 2,5-anhydro-1,6-dithio-alpha-D-glucoseptanoside (63) and 4-nitrophenyl 2,5-anhydro-1,6-dithio-alpha-D-glucoseptanoside (66), respectively. The 4-cyano group of 63 was transformed into the 4-aminothiocarbonyl, and the 4-(methylthio)(imino)methyl derivative and the 4-nitro group of 66 into the acetamido derivative. All of these thioglycosides displayed a stronger oral antithrombotic effect in rats compared with beciparcil, used as reference.     

Characterization of lyso-galactolipids, C-2 and C-3 O-acyl trigalactosylglycerol isomers, obtained from the lichenized fungus Dictyonema glabratum

A mixture of two lyso isomers of a galactolipid was obtained from Dictyonema glabratum. Aqueous hydrolysis gave rise to galactose and glycerol in a 3:1 molar ratio. ESI-MS spectroscopy gave, in the positive-ion mode, a pseudomolecular ion at m/z 839 and daughter ions with m/z 677, 600, 515 and 353, suggesting three galactosyl units linked to a glycerol moiety, substituted by one O-acyl group. 1D and 2D NMR experiments were used to characterize the glycolipid, and HMQC examination showed three anomeric signals, corresponding to two alpha-Galp and one beta-Galp residue liked to glycerol. The glycolipid structure was shown to be O-alpha-D-Galp-(1-->6)-O-alpha-D-Galp-(1-->6)-O-beta-D-Galp-(1<-->1)-2- and -3-monoacyl-D-glycerol, the latter structures not having been previously found in nature. The fatty acid composition was determined by GC-MS of derived methyl esters: that of palmitic acid C(16:0) was the most abundant, although the presence of C(12:0), C(14:0), C(16:1) and C(18:0) esters was observed.