Selective epimerization of L-chiro-inositol to L-muco- and D-chiro-inositol derivatives.

In a one step procedure, L-1-O-benzyl-2-O-methyl-chiro-inositol (1) was acetalized to the L-muco-inositol derivatives 2, 3 and D-2-O-benzyl-3-O-cyclohexylcarbamoyl-4-deoxy-4-(N,N'-dicyclohexylureido)-1-O-methyl-5,6-O-trichloroethylidene-chiro-inositol (4). Complete conversion of L-1-O-benzyl-6-O-cyclohexylcarbamoyl-3-O-formyl-2-O-methyl-4,5-O-trichloroethylidene-muco-inositol (3) into L-1-O-benzyl-6-O-cyclohexylcarbamoyl-2-O-methyl-4,5-O-trichloroethylidene-muco-inositol (2) is feasible by deformylation in boiling methanolic triethylamine. Furthermore, stepwise deprotection of 2 and 4 is described. Thus, compounds 5, 10, and 7 were obtained by decarbamoylation of 2, 4, and 6, respectively, with boiling methanolic sodium methoxide. The trichloroethylidene group of L-1-O-benzyl-2-O-methyl-4,5-O-trichloroethylidene-muco-inositol (5) was removed in a two step procedure (hydrodechlorination-deacetalization) via the ethylidene acetal 7 to give L-1-O-benzyl-2-O-methyl-muco-inositol (9). On refluxing D-chiro-inositol derivative 4 with 99% acetic acid, the ureido moiety was cleaved generating D-2-O-benzyl-4-cyclohexylamino-3-O-cyclohexylcarbamoyl-4-deoxy-1-O-methyl-5,6-O-trichloroethylidene-chiro-inositol (11). By contrast, cleavage of the ureido moiety of 10 was relatively difficult. The corresponding D-2-O-benzyl-4-cyclohexylamino-4-deoxy-1-O-methyl-5,6-O-trichloroethylidene-chiro-inositol (12) was only formed in small amounts. The structures of 1, 3 and 10 were confirmed by X-ray analysis.     

Synthesis of sorbistin analogues

D-Galactose was converted into the glycosylating agents 4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alpha-D-glucopyranosyl chloride (11) and the methyl beta-D-thiopyranoside 19. Condensation of 11 with 2,5-diazido-1,6-di-O-benzoyl-2,5-di-deoxy-L-iditol in the presence of mercury salts gave 24% of 2,5-diazido-3-O-(4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alp ha-D- glucopyranosyl)-1,6-di-O-benzoyl-2,5-dideoxy-L-iditol. Methyl trifluoromethanesulfonate-promoted glycosylation of 1,3-diazido-2-O-benzyl-1,3-dideoxy-5,6-O-isopropylidene-D-gulit ol with 19 in the presence of 2,6-di-tert-butyl-4-methylpyridine gave 1,3-diazido-4-O-(4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alp ha-D- glucopyranosyl)-2-O-benzyl-1,3-dideoxy-5,6-O-isopropylidene-D-gulitol (42), whereas, in the absence of base, migration of the O-isopropylidene group occurred, affording 1,3-diazido-6-O-(4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alp ha-D- glucopyranosyl)-2-O-benzyl-1,3-dideoxy-4,5-O-isopropylidene-D-gulitol in addition to 42.     

A precursor to the beta-pyranosides of 3-amino-3,6-dideoxy-D-mannose (mycosamine).

SN2-type reaction of 3-O-(1-imidazyl)sulfonyl-1,2:5,6-di-O-isopropylidene-alpha-D-gluco furanose with benzoate gave the 3-O-benzoyl-alpha-D-allo derivative 2, which was hydrolysed to give the 5,6-diol 3. Compound 3 was converted into the 6-deoxy-6-iodo derivative 4 which was reduced with tributylstannane, and then position 5 was protected by benzyloxymethylation, to give 3-O-benzoyl-5-O-benzyloxymethyl-6-deoxy-1,2-O-isopropylidene-alpha -D- allofuranose (6). Debenzoylation of 6 gave 7, (1-imidazyl)sulfonylation gave 8, and azide displacement gave 3-azido-5-O-benzyloxymethyl-3,6-dideoxy- 1,2-O-isopropylidene-alpha-D-glucofuranose (9, 85%). Acetolysis of 9 gave 1,2,4-tri-O-acetyl-3-azido-3,6-dideoxy-alpha,beta-D-glucopyranose (10 and 11). Selective hydrolysis of AcO-1 in the mixture of 10 and 11 with hydrazine acetate (----12), followed by conversion into the pyranosyl chloride 13, treatment with N,N-dimethylformamide dimethyl acetal in the presence of tetrabutylammonium bromide, and benzylation gave 3-azido-4-O-benzyl-3,6-dideoxy-1,2-O-(1-methoxyethylidene)-alpha-D -glucopyranose (15). Treatment of 15 with dry acetic acid gave 1,2-di-O-acetyl-3-azido-4-O-benzyl-3,6-dideoxy-beta-D-glucopyranose (16, 86% yield) that was an excellent glycosyl donor in the presence of trimethylsilyl triflate, allowing the synthesis of cyclohexyl 2-O-acetyl-3-azido-4-O-benzyl-3,6-dideoxy-beta-D-glucopyranoside (17, 90%).(ABSTRACT TRUNCATED AT 250 WORDS)     

A convenient synthetic route to the disaccharide repeating-unit of peptidoglycan

Glycosylation of the readily accessible benzyl 2-acetamido-6-O-benzyl-2-deoxy-3-O-[(R)-1-(methoxycarbonyl)ethyl]-alpha- D- glucopyranoside with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl chloride (2), using the silver triflate method in the absence of a base, afforded 65-70% of the fully protected [beta-D-GlcNPhth-(1----4)-MurNAc] methyl ester derivative 4, the structure of which was ascertained on the basis of 500-MHz 1H-n.m.r. data. 2,2'-Dideoxy-2,2'-diphthalimido-beta,beta-trehalose hexa-acetate was a by-product. Removal of the Phth group from 4, followed by acetylation, yielded 90% of the acetylated 1,6-di-O-benzyl derivative 5, which, on saponification and catalytic hydrogenation, afforded 2-acetamido-4-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-3-O-[(R)-1- carboxyethyl]-2-deoxy-D-glucopyranose. Similarly, 5 was converted into the acetylated methyl ester derivative, which, on selective removal of the methyl ester group, gave benzyl 2-acetamido-4-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D- glucopyranosyl)-6-O-benzyl-3-O-[(R)-1-carboxyethyl]-2-deoxy-alpha-D- glucopyranoside. An alternative route for the preparation of 2 is described.     

Synthesis of some monodeoxyfluorinated methyl and 4-nitrophenyl alpha-D-mannobiosides and a related 4-nitrophenyl alpha-D-mannotrioside

Treatment of methyl 3,4,6-tri-O-benzyl-2-O-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-alpha -D- mannopyranoside with N,N-diethylaminosulfur trifluoride (Et2NSF3), followed by O-deacetylation and catalytic hydrogenolysis, afforded methyl 2-O-(6-deoxy-6-fluoro-alpha-D-mannopyranosyl)-alpha-D-mannopyranoside (8). Methyl 6-deoxy-6-fluoro-2-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside (11) was similarly obtained from methyl 3-O-benzyl-2-O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl-alpha-D- mannopyranoside. 1,2,3,4-Tetra-O-acetyl-6-deoxy-6-fluoro-beta-D-mannopyranose (13), used for the synthesis of the 4-nitrophenyl analogs of 8 and 11, as well as their 3-O-linked isomers, was obtained by treatment of 1,2,3,4-tetra-O-acetyl-beta-D-mannopyranose with Et2NSF3. Treatment of 13 with 4-nitrophenol in the presence of tin(IV) chloride, followed by sequential O-deacetylation, isopropylidenation, acetylation, and cleavage of the acetal group, afforded 4-nitrophenyl 4-O-acetyl-6-deoxy-6-fluoro-alpha-D-mannopyranoside (18). Treatment of 13 with HBr in glacial acetic acid furnished the 6-deoxy-6-fluoro bromide 19. Glycosylation of diol 18 with 20 gave 4-nitrophenyl 4-O-acetyl-6-deoxy-6-fluoro-3-O- (21) and -2-O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)-alpha-D- mannopyranoside (23) in the ratio of approximately 2:1, together with a small proportion of a branched trisaccharide. 4-Nitrophenyl 4,6-di-O-acetyl-alpha-D-mannopyranoside was similarly glycosylated with bromide 19 to give 4-nitrophenyl 4,6-di-O-acetyl-3-O- and -2-O-(2,3,4-tri- O-acetyl-6-deoxy-6-fluoro-alpha-D-mannopyranosyl)-alpha-D-mannopyranosid e. The various di- and tri-saccharides were O-deacetylated by Zemplén transesterification.     

A regio- and stereo-controlled synthesis of beta-D-Glcp NAc6SO3-(1----3)-beta-D-Galp6SO3-(1----4)-beta-D-GlcpNAc 6SO3- (1----3)-D-Galp, a linear acidic glycan fragment of keratan sulfate I

A stereocontrolled synthesis of beta-D-GlcpNAc6SO3-(1----3)-beta-D-Galp6SO3-(1----4)-beta-D- GlcpNAc6SO3- (1----3)-D-Galp, was achieved by use of benzyl O-(2-acetamido-3,4 di-O-benzyl-2-deoxy-6-O-p-methoxyphenyl-beta-D- glucopyranosyl)-(1----3)-O-(2,4-di-O-tert-butyldiphenylsilyl-beta- D- galactopyranosyl-(1----4)-O-(2-acetamido-3-O-benzyl-2-deoxy-6-O-p-methox yphenyl - beta-D-glucopyranosyl)-(1----3)-2,4,6-tri-O-benzyl-beta-D-galactopyranos ide as a key intermediate, which was in turn prepared by employing two glycosyl donors, 3,4-di-O-benzyl-2-deoxy-6-O-p-methoxyphenyl-2-phthalimido-beta-D- glucopyranosyl trichloroacetimidate and O-(3,6-di-O-acetyl-2,4-di-O-benzyl-beta-D-galactopyranosyl)-(1----4)-3-O - benzyl-2-deoxy-6-O-p-methoxyphenyl-2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate, and a glycosyl acceptor, benzyl 2,4,6-tri-O-benzyl-beta-D-galactopyranoside.     

Synthesis of modified tetrasaccharide sequences of N-glycoproteins

The tetrasaccharides O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D- mannopyranosyl-(1----6)]-O-(4-deoxy-beta-D-lyxo-hexopyranosyl)-(1- ---4)-2- acetamido-2-deoxy-alpha, beta-D-glycopyranose (22) and O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D-mannopyranosyl-(1----6)]-O- beta-D-talopyranosyl-(1----4)-2-acetamido-2-deoxy-alpha, beta-D- glucopyranose (37), closely related to the tetrasaccharide core structure of N-glycoproteins, were synthesized. Starting with 1,6-anhydro-2,3-di-O-isopropylidene-beta-D-mannopyranose, the glycosyl donors 3,6-di-O-acetyl-2-O-benzyl-2,4-dideoxy-alpha-D-lyxo- hexopyranosyl bromide (10) and 3,6-di-O-acetyl-2,4-di-O-benzyl-alpha-D-talopyranosyl bromide (30), were obtained in good yield. Coupling of 10 or 30 with 1,6-anhydro-2-azido-3-O-benzyl-beta-D-glucopyranose to give, respectively, the disaccharides 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2-O-benzyl-4 -deoxy- beta-D-lyxo-hexopyranosyl)-beta-D-glucopyranose and 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2,4-di-O-ben zyl- beta-D-talopyranosyl)-beta-D-glucopyranose was achieved with good selectivity by catalysis with silver silicate. Simultaneous glycosylation of OH-3' and OH-6' of the respective disaccharides with 2-O-acetyl-3,4,6-tri-O-benzyl-alpha-D-mannopyranosyl chloride yielded tetrasaccharide derivatives, which were deblocked into the desired tetrasaccharides 22 and 37.     

An efficient synthesis of 3-fluoro-5-thio-xylofuranosyl nucleosides of thymine, uracil, and 5-fluorouracil as potential antitumor or/and antiviral agents

1,2:5,6-Di-O-isopropylidene-alpha-D-glucofuranose by the sequence of mild oxidation, reduction, fluorination, periodate oxidation, borohydride reduction, and sulfonylation gave 3-deoxy-3-fluoro-1,2-O-isopropylidene-5-O-p-toluenesulfonyl-alpha-D-xylofuranose (5). Tosylate 5 was converted to thioacetate derivative 6, which after acetolysis gave 1,2-di-O-acetyl-5-S-acetyl-3-deoxy-3-fluoro-5-thio-D-xylofuranose (7). Condensation of 7 with silylated thymine, uracil, and 5-fluorouracil afforded nucleosides 1-(5-S-acetyl-3-deoxy-3-fluoro-5-thio-beta-D-xylofuranosyl) thymine (8), 1-(5-S-acetyl-3-deoxy-3-fluoro-5-thio-beta-D-xylofuranosyl) uracil (9), and 1-(5-S-acetyl-3-deoxy-3-fluoro-5-thio-beta-D-xylofuranosyl) 5-fluorouracil (10). Compounds 8, 9, and 10 are biologically active against rotavirus infection and the growth of tumor cells.     

Pregnane steroidal glycosides and their cytostatic activities

Four new steroidal glycosides such as 3-O-6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl-(1 → 4)-β-D-cymaropyranosyl-(1 → 4)-β-D-cymaropyranoside-12-β-tigloyl-14-β-hydroxy-17-β-pregnane (1), 3-O-6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl-(1 → 4)-β-D-cymaropyranosyl-(1 → 4)-β-D-cymaropyranoside-12-β-(2'-amino)-benzoyl-14-β-hydroxy-17-β-pregnane (2), 3-O-6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl-(1 → 4)-β-D-cymaropyranosyl-(1 → 4)-β-D-cymaropyranoside-12-β-14-β-dihydroxy-17-α-pregnane (3) and 3-O-6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl-(1 → 4)-β-D-cymaropyranosyl-(1 → 4)-β-D-cymaropyranoside-12-β-14-β-dihydroxy-17-β-pregnane (4) were isolated from the aerial parts of Ceropegia fusca Bolle (Asclepiadaceae), a crassulacean acid metabolism plant, an endemic species to the Canary Islands that has been used in traditional medicine as a cicatrizant, vulnerary and disinfectant. The dichloromethane extract exhibited significant cytostatic activity against HL-60, A-431 and SK-MEL-1 cells, human leukemic, epidermoid carcinoma and melanoma cells, respectively. As shown in Table I, compounds 1 and 2 showed very similar IC(50) values. The acetylation of 1 to give the diacetate 5 increases 5-fold the cytotoxicity against HL-60 cells. Compounds 3 and 4 did not show cytotoxicity at the assayed concentrations. With respect to the compounds containing only the steroid ring (6-8), the presence of a charged O-amino-benzoyl but not a tigloyl group improved the cytotoxicity.     

Chemical modification of the C-6 substituent in the carbohydrate moiety of N-acetylmuramoyl-L-alanyl-D-isoglutamine (MDP), and the immunoadjuvant activity

N-Acetyl-6-O-mesyl-, -6-O-methyl-, and -4,6-di-O-methyl-muramoyl-L-alanyl-D-isoglutamine and N-acetyl-6-chloro-, -6-bromo-, and -6-azido-6-deoxymuramoyl-L-alanyl-D-isoglutamine were synthesized from benzyl 2-acetamido-2-deoxy-3-O-[D-1-(methoxycarbonyl) ethyl]-alpha-D-glucopyranoside and its 6-O-mesyl derivative. The immunoadjuvant activity of the products was examined, in order to clarify the structural requirements for the activity of the carbohydrate moiety in N-acetylmuramoyl-L-alanyl-D-isoglutamine.     

A common sugar as model for many-sided natural product modification. From D-fructose via Dtagatose to 2-C-chlorodifluoro-methylated D-arabinopyranos-5-ulose derivatives

Starting with 3,4-O- [(R)-2,2,2-trichloroethylidene]-1,2-O-isopropylidene- beta-D- tagatopyranose 2 obtained from 1,2-O-isopropylidene-beta-D-fructopyranose 1 by a non-classical one-step acetalization with chloral/DC~, the fluoroalkylated glyeosyl donors 15 and 17 were synthesised in 3~4 steps. By this sequence, one stereogenic center was inverted, one new chiral center was introduced, and one stereogenic center, for the time being eliminated, was later re-introduced. The glycals 11 and 12, key intermediates of the synthesis sequence, were accessible from triflate precursors (e. g., 10) by treatment with DBU. Corresponding halogeno-(6,7), tosyl-(5, 8), or mesyl-(9) precursors were unsuitable. The stereaselective introduction of a chlorodifluoromethyl group was realised by dithionite-mediated CF2C1Br-addition to the glycal double bond. Subsequently, either the chlorodifluoromethylated glyeosyl bromide (13) or the corresponding pyraneses (14 and 16) were isolated. The latter were still acetylated to the 1-O-acetyl derivatives 15 and 17, respectively. An x-ray analysis is given for the 5-O-tosylate 8.     

A concise synthesis of 3-fluoro-5-thio-xylo- and glucopyranoses, useful precursors towards their corresponding pyranonucleoside derivatives

The chemical synthesis of 1,2,4-tri-O-acetyl-3-deoxy-3-fluoro-5-thio-D-xylopyranose, 1,2,4,6-tetra-O-acetyl-3-deoxy-3-fluoro-5-thio-alpha-D-glucopyranose and their corresponding nucleosides of thymine is described. Treatment of 3-fluoro-5-S-acetyl-5-thio-D-xylofuranose, obtained by hydrolysis of the isopropylidene group of 3-fluoro-1,2-O-isopropylidene-5-S-acetyl-5-thio-D-xylofuranose, with methanolic ammonia and direct acetylation, led to triacetylated 3-deoxy-3-fluoro-5-thio-D-xylopyranose. Condensation of acetylated 3-fluoro-5-thio-D-xylopyranose with silylated thymine afforded the corresponding nucleoside. Selective benzoylation and direct methanesulfonylation of 3-fluoro-1,2-O-isopropylidene-alpha-D-glucofuranose gave the 6-O-benzoyl-5-O-methylsulfonyl derivative, which on treatment with sodium methoxide afforded the 5,6-anhydro derivative. Treatment of the latter with thiourea, followed by acetolysis, gave the 3-fluoro-5-S-acetyl-6-O-acetyl-1,2-O-isopropylidene-5-thio-alpha-D-glucofuranose. 3-fluoro-5-S-acetyl-6-O-acetyl-5-thio-D-glucofuranose, obtained after hydrolysis of 5-thiofuranose isopropylidene, was treated with ammonia in methanol and directly acetylated, giving tetraacetylated 3-deoxy-3-fluoro-5-thio-alpha-D-glucopyranose. Condensation of the latter with silylated thymine afforded the desired 3-deoxy-3-fluoro-5-thio-beta-D-glucopyranonucleoside analogue.     

First derivatives of myo-inositol 1,4,6-trisphosphate modified at positions 2 and 3: structural analogues of D-myo-inositol 1,4,5-trisphosphate

Novel, structurally modified potential mimics of the second messenger D-myo-inositol 1,4,5-trisphosphate, based on the biologically active regioisomer D-myo-inositol 1,4,6-trisphosphate, were synthesised. DL-5-O-Benzyl-1,4,6-tri-O-p-methoxybenzyl-myo-inositol was the key intermediate for the preparation of the following compounds: DL-3-deoxy-, DL-3-deoxy-2-O-methyl-, DL-3-O-(2-hydroxyethyl)-, DL-3-O-(3-hydroxypropyl)- and DL-3-O-(4-hydroxybutyl)-myo-inositol 1,4,6-trisphosphate. DL-1,4,6-Tri-O -allyl-5-O-benzyl-myo-inositol was used to prepare DL-2-O-methyl-myo-inositol 1,4,6-trisphosphate. Deoxy-compounds were prepared by reduction of the corresponding tosylated intermediate using Super Hydride. The hydroxyalkyl groups were introduced at the C-3 of myo-inositol using the corresponding benzyl protected hydroxy alkyl bromide via the cis-2,3-O-dibutylstannylene acetal. Methylation and benzylation at C-2 was accomplished using methyl iodide and benzyl bromide, respectively, in the presence of sodium hydride. Deblocking of p-methoxybenzyl groups was accomplished with TFA in dichloromethane and the allyl groups were removed by isomerisation to the cis-prop-1-enyl derivative, which was hydrolysed under acidic conditions to give the corresponding 1,4,6-triol. The 1,4,6-triols were phosphitylated with the P(III) reagent bis(benzyloxy)(diisopropylamino)phosphine in the presence of 1H-tetrazole then oxidised with 3-chloroperoxybenzoic acid followed by deblocking by hydrogenolysis to give DL-2-O-methyl-, DL-3-O-deoxy-, DL-3-O-deoxy-2-O-methyl-, DL-3-O-(2-hydroxyethyl)-, DL-3-O-(3-hydroxypropyl)- and DL-3-O-(4-hydroxybutyl)-myo-inositol 1,4,6-trisphosphate, respectively.     

Synthesis of methyl glycoside derivatives of tri- and penta-saccharides related to the antithrombin III-binding sequence of heparin, employing cellobiose as a key starting-material

Two key synthons for the title pentasaccharide derivative, methyl O-(methyl 2-O-benzoyl-3-O-benzyl-alpha-L-idopyranosyluronate)-(1----4)-6-O-acetyl- 2-azido - 3-O- benzyl-2-deoxy-beta-D-glucopyranoside and O-(methyl 2,3-di-O-benzyl-4-O- chloroacetyl-beta-D-glucopyranosyluronate)-(1----4)-3,6-di-O-acetyl-2-az ido-2- deoxy-alpha-D- glucopyranosyl bromide, were prepared from a common starting material, cellobiose. They were coupled to give a tetrasaccharide derivative that underwent O-dechloroacetylation to the corresponding glycosyl acceptor. Its condensation with the known 6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl bromide afforded a 77% yield of suitably protected pentasaccharide, methyl O-(6-O- acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl)-(1----4)- O- (methyl 2,3- di-O-benzyl-beta-D-glucopyranosyluronate)-(1----4)-O-(3,6-di-O-acetyl-2- azido-2 - deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(methyl 2-O-benzoyl-3-O-benzyl-alpha-L- idopyranosyluronate)- (1----4)-6-O-acetyl-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranoside. Sequential deprotection and sulfation gave the decasodium salt of methyl O-(2- deoxy-2-sulfamido-6-O-sulfo-alpha-D-glucopyranosyl)-(1----4)-O-(be ta-D- glucopyranosyl-uronic acid)-(1----4)-O-(2-deoxy-2-sulfamido-3,6-di-O-sulfo-alpha-D-gluco pyranosyl)- (1----4)-O-(2-O-sulfo-alpha-L-idopyranosyluronic acid)-(1----4)-2-deoxy-2- sulfamido-6-O- sulfo-beta-D-glucopyranoside (3). In a similar way, the trisaccharide derivative, the hexasodium salt of methyl O-(2-deoxy-2-sulfamido-6-O-sulfo-alpha-D- glucopyranosyl)- (1----4)-O-(beta-D-glucopyranosyluronic acid)-(1----4)-2-deoxy-2-sulfamido-3,6- di-O- sulfo-alpha-D-glucopyranoside (4) was synthesized from methyl O-(6-O-acetyl-2- azido- 3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(methyl 2,3-di-O- benzyl-beta- D-glucopyranosyluronate)-3,6-di-O-acetyl-2-azido-2-deoxy-alpha-D- glucopyranoside. The pentasaccharide 3 binds strongly to antithrombin III with an association constant almost equivalent to that of high-affinity heparin, but the trisaccharide 4 appears not to bind.     

A practical synthesis of 2-deoxy-2-fluoro-D-arabinofuranose derivatives.

A seven-step synthesis of 1,3-di-O-acetyl-5-O-benzoyl-2-deoxy-2-fluoro-D-arabinofuranose, a versatile intermediate in the synthesis of chemotherapeutically important nucleosides, was achieved from 1,2:5,6-di-O-isopropylidene-3-O-tosyl-alpha-D-allofuranose. The crucial steps were the fluorination by use of potassium fluoride in acetamide and the conversion of 6-O-benzoyl-3-deoxy-3-fluoro-D-glucofuranose into 5-O-benzoyl-2-deoxy-2-fluoro-3-O-formyl-D-arabinofuranose by periodate oxidation. Also described is the synthesis of 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)cytosine. This procedure affords good overall yields of products without formation of undesirable, isomeric intermediates and is suitable for large-scale preparations.     

Synthesis of oligosaccharides containing the X-antigenic trisaccharide (alpha-L-Fucp-(1----3)-[beta-D-Galp-(1----4)]-beta-D-GlcpNAc) at their nonreducing ends.

The "armed" methyl 2,3,4-tri-O-benzyl-1-thio-beta-L-fucopyranoside was reacted with "disarmed" phenyl O-(tetra-O-acetyl-beta-D-galactopyranosyl)-(1----4)-6-O-benzyl-2- deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside in the presence of CuBr2-Bu4NBr complex to give phenyl O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1----4)-O- [(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-(1----3])-6-O-benzyl-2-deoxy -2- phthalimido-1-thio-beta-D-glucopyranoside (6) as a novel glycosyl donor. The glycosylating capability of 6 was further examined using N-iodosuccinimide-triflic acid as a reagent. This led to the synthesis of a tetrasaccharide and a pentasaccharide incorporating the X-antigenic structure represented by 6.     

A practical route to partially protected pyrrolidines as precursors for the stereoselective synthesis of alexines

Either 3-O-benzoyl- (2a) or 3-O-benzyl-1,2-O-isopropylidene-beta-D-fructopyranose (2b) were regioselectively O-benzylated at C-4 to give 4a and 4b, respectively, which were transformed into 5-azido-3-O-benzoyl-4-O-benzyl- (6a) and 5-azido-3,4-di-O-benzyl-5-deoxy-1,2-O-isopropylidene-alpha-L-sorbopyranose (6b) by nucleophilic displacement of the corresponding 5-O-mesyl derivatives 5a and 5b by sodium azide in DMF, respectively. Compound 6b was also prepared from 4b in one step by the Mitsunobu methodology. Deacetonation of 6a and 6b gave the partially protected free azidouloses 8a and 8b, respectively, that were protected as their 1-O-TBDPS derivatives 9a and 9b. Hydrogenation of 9b over Raney nickel gave stereoselectively (2R,3R,4R,5S)-3,4-dibenzyloxy-2'-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (12) which was identified by transformation into the well known (2R,3R,4R,5S)-3,4-dihydroxy-2,5-bis(hydroxymethyl)pyrrolidine (1, DGDP).     

Etoposide: a new approach to the synthesis of 4-O-(2-amino-2-deoxy-4,6-O-ethylidene-beta-D-glucopyranosyl)-4'-O- demethyl-4-epipodophyllotoxin

Synthesis of 3-O-acetyl-2-benzyloxycarbonylamino-2-deoxy-4,6-O-ethylidene- alpha-(7 alpha) and-beta-D-glucopyranose (7 beta) and their 3-O-chloroacetyl analogues (11 alpha and 11 beta) are described. Condensation (BF3-etherate, ethyl acetate, -20 degrees) of 7 alpha with 4'-O-benzyloxycarbonyl-4'-O-demethyl-4-epipodophyllotoxin (8) afforded mainly the beta-glycoside 9 beta (alpha, beta-ratio 1:9). Condensation of 11 alpha beta with 8 or the 4'-O-chloroacetyl analogue 13 gave mainly the 4-O-(2-benzyloxycarbonylamino-3-O-chloroacetyl-2-deoxy-4,6-O-ethyl idene-beta-D- glucopyranosyl)-epipodophyllotoxin 12 beta or 15 beta. Glycosidation of podophyllotoxin (14) with 11 alpha beta (during which the aglycon epimerized at C-4 under the action of BF3-etherate) afforded alpha- (16 alpha) and beta-glycoside (16 beta) in the ratio 1:5. Removal of the chloroacetyl groups from 12 beta, its alpha analogue 12 alpha, and 15 beta gave the 4-O-(2-benzyloxycarbonylamino-2-deoxy-4,6-O-ethylidene-alpha-(17 alpha) and -beta-D-glucopyranosyl)-4'-O-demethyl-epipodophyllotoxins (17 beta and 20 beta), respectively. Hydrogenolysis of the benzyloxycarbonyl groups then gave 4-O-(2-amino-2-deoxy-4,6-O-ethylidene-alpha- (18 alpha) and -beta-D-glucopyranosyl)-4'-O-demethyl-4-epipodophyllotoxin (18 beta). Reductive alkylation of 18 beta and 18 alpha afforded the 2"-deoxy-2"-dimethylamino-etoposide 3 and its alpha analogue 19 alpha.     

Polyoxypregnane glycosides from Caralluma retrospiciens

Six related polyoxypregnane glycosides were isolated and characterised from Caralluma retrospiciens leaves. The compounds were identified as 12beta-benzoyloxy-8beta,14beta-dihydroxypregn-20-one-3-O-[3-O-methyl-6-deoxy-beta-D-allopyranosyl-(1 --> 4)-beta-D-cymaropyranosyl-(1 --> 4)-]-beta-D-cymaropyranoside], 12beta-benzoyloxy-8beta,14beta-dihydroxypregn-20-one-3-O-[beta-D-glucopyranosyl-(1 --> 4)-3-O-methyl-6-deoxy-beta-D-allopyranosyl-(1 --> 4)-beta-D-cymaropyranosyl-(1 --> 4)-beta-D-cymaropyranoside], 12beta-benzoyloxy-8beta,14beta-dihydroxypregn-20-one-3-O-[beta-D-glucopyranosyl-(1 --> 4)-3-O-methyl-6-deoxy-beta-D-galactopyranosyl-(1 --> 4)-3-O-methyl-6-deoxy-beta-D-galactopyranoside], 12beta-benzoyloxy-8beta,14beta-dihydroxypregn-20-one-3-O-[beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl-(1 --> 4)-3-O-methyl-6-deoxy-beta-D-galactopyranosyl-(1 --> 4)-3-O-methyl-6-deoxy-beta-D-galactopyranoside], 12beta-benzoyloxy-11alpha-isovaleroyloxy-8beta,14beta-dihydroxypregn-20-one-3-O-[beta-D-glucopyranosyl-(1 --> 4)-3-O-methyl-6-deoxy-beta-D-galactopyranosyl-(1 --> 4)-3-O-methyl-6-deoxy-beta-D-galactopyranoside], and 12beta-benzoyloxy-11alpha-isovaleroyloxy-8beta,14beta-dihydroxypregn-20-one-3-O-[beta-D-glucopyranosyl (1 --> 4)-3-O-methyl-6-deoxy-beta-D-allopyranosyl-(1 --> 4)-beta-D-cymaropyranosyl-(1 --> 4)-beta-D-cymaropyranoside]. The structures were determined by detailed analysis of one- and two-dimensional NMR spectra as well as by chemical means. The compounds showed cytotoxic activities towards brine shrimp having IC50 values of 1.19 x 10(-4), 8.83 x 10(-5), 2.64 x 10(-4), 2.26 x 10(-4), 2.39 x 10(-4) and 1.70 x 10(-4) M, respectively. This is the first report of the isolation of these compounds from a natural source.     

Preparation of 1,2-O-isopropylidene derivatives of alpha-D-galactoseptanose, beta-L-altroseptanose, and 3-O-methyl-alpha-D-guloseptanose

Displacement of the tosyloxy group in 5-O-benzyl-1,2-O-isopropylidene-4-O-(p-toluenesulfonyl)-alpha-D-glucoseptanose has yielded derivatives of 1,2-O-isopropylidene-alpha-D-galactoseptanose. Acid catalysed acetonation then gave 1,2:3,4-di-O-isopropylidene-alpha-D-galactoseptanose or 1,2;4,5-di-O-isopropylidene-alpha-D-galactoseptanose using lower acid concentrations. Reduction of the ketone derived from 1,2:3,4-O-isopropylidene-alpha-D-septanose gave 1,2;3,4-di-O-isopropylidene-beta-L-altroseptanose. Reaction of 3,4-anhydro-5-O-benzyl-1,2-O-isopropylidene-alpha-D-galactoseptanose with sodium methoxide gave 5-O-benzyl-1,2-O-isopropylidene-4-O-methyl-alpha-D-glucoseptanose and 5-O-benzyl-1,2-O-isopropylidene-3-O-methyl-alpha-D-guloseptanose. Solution-state conformations of these compounds have been deduced from their 1H NMR spectra.