摘要:

The title trisaccharides were synthesized from a common trisaccharide thioglycoside derivative, which was, in turn, prepared from monosaccharide thioglycoside precursors. An acyclic analogue, methyl 3-O-(α-D-galacto-pyranosyl)-6-O-[(2′-hydroxyethyl)oxymethyl]-α-D-glucopyranoside, which carries a 2′-hydroxyethyloxymethyl group in place of the 6-O-galactosyl residue, was also synthesized.

ISSN:0732-8303    

DOI:10.1080/07328308808058925

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Regioselective silylation of α-cyclodextrin withtert-butyl-dimethylsilyl chloride inN, N-dimethylformamide in the presence of imidazole gave, in 75% yield, the hexakis(6-O-tert-butyldimethylsilyl) derivative 2, which was transformed into the hexakis(2,3-di-O-methyl, 6-O-methyl, 2,3-di-O-propyl, and 2,3-di-O-acetyl) derivatives. On methanesulfonylation and p-toluenesulfonylation, the hexakis(2,3-di-O-acetyl) derivative16afforded the hexakis(2,3-di-O-acetyl-6-O-methylsulfonyl17and 2,3-di-O-acetyl-6-O-p -tolylsulfonyl18) derivatives, respectively. Nucleophilic displacement of17and18with iodide, bromide, chloride, and azide ions afforded the hexakis(6-deoxy-6-iodo19, 6-bromo-6-deoxy, 6-chloro-6-deoxy, and 6-azido-6-deoxy) derivatives, respectively, of α-cyclodextrin dodeca-acetate. The hexakis (2, 3-di-O-acetyl-6-deoxy) derivative was prepared from19. Selective glucosylation of16with 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl bromide under catalysis by halide ion, followed by removal of protecting groups, furnished 6-O-α-D-glucopyranosyl-α-cyclodextrin.

ISSN:0732-8303    

DOI:10.1080/07328308808058926

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Selective glycosylation of benzyl 4,6-O-benzylidene-β-D-galacto-pyranoside (1) with 1.5 mole equivalent of 2,3,4,6-tetra-O-binzyl-α-D-galactopyranosyl bromide (2) catalyzed by halide ion gave the (1→2)-α-(5) and (l→3)-α-D-linked disaccharide (7) derivatives in 22 and 40% yields, respectively. The D-galactose unit at the reducing end of 2-O-α-D-galactopyranosyl-D-galactose [11) at equilibrium in D2O was shown By13C NMR spectroscopy to exist in the pyranose and furanose forms in the ratio of ∼2:1.

ISSN:0732-8303    

DOI:10.1080/07328308808058927

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Sequential tritylation, benzoylation and detritylation of D-glucose, followed by resolution of the crude product by chromatograpEy gave crystalline 1,2,3,4-tetra-O-benzoyl-α- (1) and β-D-glucopyranose (2). Compound 1, 2, and the corresponding methyl α-glycoside 5 were treated with dimethylaminosulfur trifluoride (methyl DAST) to give, respectively, the 6-deoxy-6-fluoro derivatives 3, 4, and 6. Crystalline 2,3,4-tri-O-benzoyl-6-deoxy-6-fluoro-α-D-glucopyranosyl chloride (10) could be obtained from either 3, 4, or 5 by reaction with dichloromethyl methyl ether in the presence of anhydrous zinc chloride. Silver trifluoromethanesulfonate-promoted reaction of 10 with methyl 2-O-(9) and 3-O-benzyl-4,6-O-benzylidene-α-D-glucopyranoside (8) gave the corresponding, (β-linked disaccharidës in high yield. Subsequent deprotection afforded the 6′-deoxy-6′-fluoro derivatives of methyl α-sophoroside (13) and methyl 6′ -deoxy-o′-fluoro-α-laminaribioside (16). Condensation of 8 and 9 with 6-O-acetyl-2,3,4-tri-O-benzyl-α-D-glucopyranosyl chloride in the presence of silver perchlorate was highly stereoselective and produced the α-linked disaccharidës 17 and 21, respectively, in excellent yield. Deacetylation of 17 and 21, followed by fluorination of the resulting alcohols 18 and 22 with methyl DAST and subsequent hydrogenolysis, gave 6′-deoxy-6′-fluoro derivatives of methyl α-kojibioside and methyl α-nigeroside 20 and 24, respectively.

ISSN:0732-8303    

DOI:10.1080/07328308808058928

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Starting from L-rhamnose, benzyl 2,4-di-O-benzyl-6-deoxy-α-L-talopyranoside (7) was prepared by hydrogenolysis of a dioxolane-type benzylidene acetal and used as the aglycon to prepare 2-acetamido-2-deoxy-6-D-glucopyranosyl-(1–3)-6-deoxy-L-talose (13) and the title trisacchafide (20). Due to fast interconvirsion between the α-, β- -pyranose/furanose forms at the reducing end of the molecule in aqueous solutions, the di- and trisaccharides occur as mixtures of four isomers all in significant concentration. By two-dimensional (20) methods, the proton (400) and carbon (100 MHz) NMR spectra of the individual tri-saccharide isomers were completely assigned and interpreted in terms of stereochemistry of the 6-deoxy-L-talose residue.

ISSN:0732-8303    

DOI:10.1080/07328308808058929

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Hexatriosyl fluorides3and4were prepared from the known trisaccharides8and13, respectively. These compounds were reacted with the sphingosine derivative2to afford coupled products22and25which, in turn, were converted into the protected glycosphingolipids23and26after reduction and acylation. Compound2was found to be a better substrate than the protected ceramide1, which had been used previously. Compound23was transformed into the lacto-N-triosylceramide24.

ISSN:0732-8303    

DOI:10.1080/07328308808058930

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Glycosylation of methyl 3-O-(2-acetamido-3, 6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (2) with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide (1), catalyzed by mercuric cyanide, afforded a trisaccharide derivative, which was not separated, but directlyO-deacetylated to give methyl 3-O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-β-D-galactopyranosyl-β-D-giucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (8). Hydrogenolysls of the benzyl groups of8then furnished the title trisaccharide (9). A similar pflyccsylation of methyl 3-O-(2-acetamido-3-O-acetyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl- β-D-galactopyranoside (obtained by acetylation of4, followed by hydrolysis of the benzylidene acetal group) with bromide1gave a tribenzyl trisaccharide, which, on catalytic hydrogenolysls, furnished the isomeric trisaccharide (12). Methylation of4and2with methyl iodide-silver oxide in 1:1 dichloro-methane-N, N-dimethylformamide gave the 3-O- and 4-O-monomethyl ethers (13) and (15), respectively. Hydrogenolysis of the benzyl groups of13and15 then provided the title monomethylated disaechartdes (15) and (16), respectively. The structures of trisacchacides9and12, and disaccharides14and16were all established by13C MMR spectroscopy.

ISSN:0732-8303    

DOI:10.1080/07328308808058931

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A synthesis is described of the heptasaccharide 1, which may form part of the phytoelicitor-active glucan ofPhytopkthora megasperma f. sp. glycinea. Silver triflate was used as the promoter in Koenigs-Knorr type condensations using glycosyl bromides, each with a participating benzoyl group in the 2-position, for the synthesis of the smaller oligosaccharide fragments. For joining the larger ones, methyl triflate was used as the promoter and an oligosaccharide thioglycoside carrying a participating benzoyl group in the 2-position was used as the glycosyl donor.

ISSN:0732-8303    

DOI:10.1080/07328308808058932

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The synthesis of spacer-containing fragments of the capsular poly-saccharide of H.influenzas, comprising two and three repeating units (9aand9b, respectively), is presented. Ribosylribitol building blocks1and2were coupled with bis [1-benzotriazolyl]-2-chlorophenyl phosphate (3) to give the phosphotriester derivative5a(72%), which was selectively deprotected at O-5 of the terminal ribitol residue (cleavage of the trans-1-propenyl ether) to afford compound6a(82%). Repeated coupling of building block2with6a(chain elongation), followed by propenyl- cleavage, gave analogue6b. Both derivatives6aand6bwere coupled with spacer7(chain termination). The fully protected fragments8a(84%) and8b(49%, starting from6a) were thus obtained. Complete deprotection of8aand8bwas achieved in three steps. After purification and cation-exchange,9aand9bwere obtained in 41 and 68% yields, respectively. The structural integrity of the largest fragment (9b) was confirmed by FAB MS and various NMR spectroscopic techniques.

ISSN:0732-8303    

DOI:10.1080/07328308808058933

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Condensation of benzyl 2,3,6-trideoxy-3-trifluoroacetamido-α-L-lyxo-hexopyranoside (5) with 4-O-acetyl-3-O-benzyl-2,6-dideoxy-α-L-lyxo-hexopyranosyl bromide (10) carried out under Koenigs-Knorr conditions gave12. Total deprotection of12and N-dimethylation at C-3 led to17while selective removal of the 4-O-acetyl group led to13, a synthetic intermediate for preparing24and33. Condensation of13with di-O-acetyl-L-fucal (18) or 4-O-acetyl-L-amicetal (25) in the presence ofN-iodosuccinimide followed by hydrogenolysis of the C-2-I bond gave20and27respectively. The trisaccharide24then was obtained from20by the same sequence of reactions used to convert12into17. After deacetylation and oxidation, this set of reactions also transformed27into33.

ISSN:0732-8303    

DOI:10.1080/07328308808058934

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor