摘要:

The syntheses of galactaric acid acetate bis[alkylthio-(thiocarbonyl)]hydrazides (1,2) are described. Selective cyclisation of both hydrazide 1 and 2 was investigated. Using phosphorous oxychloride as a cyclising agent, loss of water produced 1,2,3,4-tetra-O-acetyl-1,4-bis(5-S-methyl or benzyl)-1,3,4-thiadiazol-2-yl)galacto-tetritol (3) or (4). Use of thionyl chloride lead to dehydrosulfurization and gave 1,2,3,4-tetra-O-acetyl-1,4-bis(5-S-methyl or benzyl)-1,3,4-oxadiazol-2-yl)galacto-tetritol (5) or (6). Finally, with triethyl orthoformate as the cyclising agent, compound 1 or 2 gave 3,3′-(2,3,4,5-tetra-O-acetylgalactar-1,6-dioyl)-bis-[(2-ethoxy-2,3-dihydro-5-S-methyl or benzyl)-1,3,4-thia-diazole] (7) or (8).

ISSN:0732-8303    

DOI:10.1080/07328309108543919

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The first total syntheses of sialyl-α(2→6)-lactotetraosylceramide (29, IV6NeuAcLc4Cer) and sialyl-α(2→6)-neolatotetraosylceramide (33, IV6NeuAcnLc4Cer) are described. Methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→6)-2,4-di-O-benzoyl-3-O-benzyl-1-thio-ß-D-galactopyranoside (11), the key glycosyl donor was prepared, via glycosylation of 2-(trimethylsilyl)ethyl 3-O-benzyl-ß-D-galactopyranoside (2) with the methyl α-thioglycoside 3 of N-acetylneuraminic acid, benzoylation, replacement of the 2-(trimethylsilyl)ethyl group by acetyl, and introduction of the methylthio group with (methylthio)trimethylsilane. Each coupling of 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-ß-D-glucopyranosyl)-(1→3′)-per-O-benzyl-ß-lactoside (12) or 2-(trimethylsilyl)ethyl O-(2-acetamido-3-O-acetyl-6-O-benzyl-2-deozy-ß-D-glucopyranosyl)-(1→3′)-per-O-benzyl-ß-D-lactoside (14) prepared from 12 by O-acetylation and reductive opening of the benzylidene acetal, with 11 gave the pentasaccharides 16 and 20 in good yields. Compounds 16 and 20 were converted into the corresponding α-trichloroacetimidates 19 and 24 which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (25), gave the ß-glycosides 26 and 30, respectively. Finally, 26 and 30 were transformed, via selective reduction of the azide group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into 29 and 33, respectively.

ISSN:0732-8303    

DOI:10.1080/07328309108543920

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

3-Hydrazino-5,6-diphenyl-1,2,4-triazine (1) reacts with D(−)fructose, D(+)glucose, D(−)ribose and D(−)arabinose to give the corresponding bis triazinyl hydrazones 4a and 7a. Reactions of these hydrazones with acetic anhydride and with phenyldiazonium chloride are described.

ISSN:0732-8303    

DOI:10.1080/07328309108543921

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Hydrogenolysis of 2,3,5-tri-O-benzoyl-6-O-trityl-D-galactono-1,4-lactone (2) gave the corresponding 3-deoxy-D-xylo-hexono-1,4-lactone derivative (3), which on treatment with HBr in acetic acid afforded 2,5-di-O-benzoyl-6-bromo-3,6-dideoxy-D-xylo-hexono 1,4-lactone (4). Hydrogenation of 4 led to 3,6-dideoxy-D-xylo-hexono-1,4-lactone dibenzoate (6). The overall yield of 6 from D-galactono-1, 4-lactone (1) was about 59%. Alternatively, compound 6 was prepared (67% overall yield from 1) by hydrogenolysis of 6-bromo-6-deoxy-D-galactono-1,4-lactone tribenzoate (5), obtained by treatment of 2 with HBr in dry dichloromethane. Diisoamylborane reduction of 6 gave an anomeric mixture of 2,5-di-O-benzoyl-3,6-dideoxy-α, β-D-xylo-hexofuranose (7), which onO-debenzoylation afforded 3,6-dideoxy-D-xylo-hexose (abequose, 8) whose tautomeric equilibrium was studied by13C NMR spectroscopy. Acetylation of 7 gave the 1-O-acetyl derivative (9) mainly in the β anomeric configuration. Tin (IV) chloride promoted glycosylation of 9 with methanol and ethanol afforded stereoselectively methyl (10) and ethyl 2,5-di-O-benzoyl-3,6-dideoxy-β-D-xylo-hexofuranoside (11), respectively.

ISSN:0732-8303    

DOI:10.1080/07328309108543922

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The revived interest in phenolic glycolipids of pathogenic mycobacteria is evoked by a widespread1-3use ofMycobacterium (M.) lepraespecific antigen for serodiagnosis of leprosy patients. As a consequence, a few phenolic glycolipids of other mycobacterias were isolated and structurally elucidated. Recently Vercellone and Puzo4reported the isolation of new phenolic glycolipids not yet described inM. bovisBCG. The combination of sugars in one of the glycolipids was identified as 3-O-(α-L-rhamnopyranosyl)-2-O-methyl-α-L-rhamnopyranoside (1) which is closely related to the trisaccharide segment (2) ofM. tuberculosisstrain Canetti.5The latter contains 2,3,4-tri-O-methyl-L-fucopyranosyl monosaccharide α-linked to 3′ position of 1. It has been emphasised that new found glycolipids ofM. bovisBCG could share common epitopes with those ofM. tuberculosis, thus leading to false positive immunoabsorbent assay tests during screening of tuberculosis patients. In addition, there is concern regarding the involvement of one of the new found glycolipids in the stimulation of T suppressor cells, thus adding to the conflicting results noted in the protection ofM. tuberculosisbyM. bovisBCG. In essence the new found phenolic glycolipids ofM. bovisBCG are associated with interesting but unclear biological profiles. We now report the synthesis of these closely related oligosaccharides, 1 (R = Me) and 2 (R = Me).

ISSN:0732-8303    

DOI:10.1080/07328309108543923

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The oxidative coupling of glycals with alcohols is an efficient procedure for creating an α-glycosidic bond. It can be triggered by an “I+”-reagent (iodonium di-sym-collidine perchlorate1orN-iodosuccinimide2) and occurs in a 1,2-diaxial fashion through a presumed 1,2-iodonium ion intermediate leading to 2-deoxy-2-iodo-α-glycosides. This iodoglycosylation allows the preparation of 2-deoxy-α-glycosides by reductive deiodination with tributylstannane3or nickel boride.4Considering the behavior of good leaving groups at C-2 of α-D-mannopyranosides,5the displacement of iodine by oxygen or nitrogen functions through SN2-type reactions would be difficult or impossible, unless performed with internal nucleophiles.6In contrast, a C-2 radical can be easily trapped by electron-deficient olefins7or nitrogen monoxide8giving access to C-2 branched carbohydrates and oximes, respectively. Nucleophilic radicals have also been trapped by aryldiazonium ions in a reversible manner to give azo radical cations.9In the presence of a reducing agent (Ti3+, Fe2+, Cr2+, V2+), the equilibrium is shifted towards the azo compound:

ISSN:0732-8303    

DOI:10.1080/07328309108543924

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Development of an efficient α-glycoside synthesis of sialic acids is critically significant for the syntheses of sialoglycoconjugates, especially gangliosides which carry important biological functions1in biological systems. Previously, we demonstrated2a new α-glycosylation of sialic acids by use of dimethyl(methylthio)sulfonium triflate (DMTST)3as the glycosyl promoter, the suitably protected glycosyl acceptors and the methyl 2-thioglycoside 1 of N-acetylneuraminic acid (Neu5Ac) as the donor in acetonitrile under kinetically controlled conditions, and accomplished4the syntheses of a variety of gangliosides and their analogs.

ISSN:0732-8303    

DOI:10.1080/07328309108543925

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Cyclic acetals are important and commonly used protective groups for polyhydroxy compounds,e.g., carbohydrates. The formation of cyclic acetals has been thoroughly investigated and much is now known about the factors that influence the outcome of these reactions. Several reviews have been written on this subject.1,2,3

ISSN:0732-8303    

DOI:10.1080/07328309108543926

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0732-8303    

DOI:10.1080/07328309108543927

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor