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A Lipták

Publications and source records attributed to A Lipták.

35 records · Page 2Linked to original sources
PubMed1993

Synthesis of p-trifluoroacetamidophenyl 6-deoxy-2-O-(3-O-[2-O-methyl-3-O- (2-O-methyl-alpha-D-rhamnopyranosyl)-alpha-L-fucopyranosyl]-alpha-L- rhamnopyranosyl)-alpha-L-talopyranoside: a spacer armed tetrasaccharide glycopeptidolipid antigen of Mycobacterium avium serovar 20.

The synthesis of the title tetrasaccharide glycoside 38 is reported. p-Nitrophenyl endo-3,4-O-benzylidene-6-deoxy-alpha-L-talopyranoside (4), 3-O-acetyl-2,4-di-O-benzyl-alpha-L-rhamnopyranosyl trichloroacetimidate (7), methyl 3-O-acetyl-4-O-benzyl-2-O-methyl-1-thio-beta-L-fucopyranoside (15), 3-O-acetyl-4-O-benzyl-2-O-methyl-alpha-L-fucopyranosyl bromide (16), and ethyl 3-O-acetyl-4-O-benzyl-2-O-methyl-1-thio-alpha-D-rhamnopyranoside (33) were prepared as intermediates. Compound 4 was glycosylated with imidate 7 as well as with methyl 3-O-acetyl-2,4-di-O-benzyl-1-thio-alpha-L-rhamnopyranoside (9), affording the same disaccharide derivative 8. Deacetylation of 8 gave crystalline 17. Condensation of 17 with both fucosyl donors 15 and 16 yielded the same trisaccharide derivative 18 stereoselectively. Compound 18 was also prepared by the coupling of 4 with disaccharide glycosyl donor 20. After deacetylation of 18 (-->34), methyl triflate-promoted glycosylation with compound 33 resulted in tetrasaccharide 35. Conversion of the p-nitrophenyl group of 35 into the p-trifluoroacetamidophenyl group (-->36) and removal of the protecting groups gave the title tetrasaccharide glycoside 38.

Carbohydrate Conformation↗
PubMed1993

A new approach to the chemical synthesis of the trisaccharide, and the terminal di- and mono-saccharide units of the major, serologically active glycolipid from Mycobacterium leprae.

The key intermediates for the synthesis of p-trifluoroacetamidophenyl O-(3,6-di-O-methyl-beta-D-glucopyranosyl)-(1-->4)-O-(2,3-di-O-methyl-alp ha-L- rhamnopyranosyl)-(1-->2)-3-O-methyl-alpha-L-rhamnopyranoside (15), as well as p-trifluoroacetamidophenyl O-(3,6-di-O-methyl-beta-D- glucopyranosyl)-(1-->4)-2,3-di-O-methyl-alpha-L-rhamnopyranoside (29), were the methyl and ethyl O-(2-O-benzyl-4,6-O-benzylidene-3-O-methyl-beta- D-glucopyranosyl)-(1-->4)-2,3-O-diphenylmethylene-1-thio-alpha-L- rhamnopyranosides (10 and 24). Dichloroalane treatment of 10 and 24 removed the diphenylmethylene group, liberating HO-2 and HO-3 of the rhamnopyranoside residue, and opened the benzylidene acetal regioselectively to give the 4-O-benzyl-glucopyranosyl disaccharides. Methylation of the free OH groups resulted in the tetra-O-methyl 1-thio disaccharides (12 and 26), useful as glycosyl donors. Introduction of these temporary blocking groups allowed a drastic reduction in the number of synthetic steps to the target compounds.

Antigens, Bacterial↗
PubMed1993

Synthesis of a selectively protected trisaccharide building block that is part of xylose-containing carbohydrate chains from N-glycoproteins.

The synthesis is reported of ethyl 4-O-[3-O-allyl-4,6-O-isopropylidene-2-O-(2,3,4-tri-O-acetyl-beta-D- xylopyranosyl)-beta-D-mannopyranosyl]-3,6-di-O-benzyl-2-deoxy-2-phthalim ido-1 - thio-beta-D-glucopyranoside (16), a key intermediate in the synthesis of xylose-containing carbohydrate chains from N-glycoproteins. Condensation of ethyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-beta-D- glucopyranoside (5) with 2,4,6-tri-O-acetyl-3-O-allyl-alpha-D-glucopyranosyl bromide, using silver triflate as a promoter, gave the beta-linked disaccharide derivative 8 (84%). O-Deacetylation of 8 and then isopropylidenation afforded 10, which was converted via oxidation-reduction into ethyl 4-O-(3-O-allyl-4,6-O-isopropylidene-beta-D-mannopyranosyl)-3,6-di-O-benz yl-2- deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (12). Silver triflate-promoted condensation of 12 with 2,3,4-tri-O-acetyl-alpha-D-xylopyranosyl bromide gave 16 (71%). The Xylp unit in 16 and in de-isopropylidenated 16 (17) existed in the 1C4(D) conformation, but that in O-deacetylated 17 (18) existed in the 4C1(D) conformation.

Carbohydrate Conformation↗
PubMed1990

Anomalous Zemplén deacylation reactions of 2-O-acyl-3-O-alkyl or -3-O-glycosyl derivatives of D-galactose and D-glucose: synthesis of O-alpha-D-mannopyranosyl-(1----4)-O-alpha-L-rhamnopyranosyl-(1----3)-D- galactose and an intermediate for the preparation of 2-O-glycosyl-3-O-(alpha-D-mannopyranosyl)-D-glucoses.

Treatment of 2-O-benzoyl (1) and 2-O-acetyl (5) derivatives of benzyl 4,6-benzylidene-3-O-(2,3,4-tri-O-acetyl-alpha-L-rhamnopyranosyl)-beta-D- galactopyranoside under Zemplén conditions (catalytic amount of sodium methoxide in methanol) gave partially deacylated disaccharides in which the 2-O-acyl groups were retained. Likewise, a similar result was obtained with the beta-L-rhamnopyranosyl analogue (3) of 1. This anomalous reaction was used in a synthesis of the title trisaccharide (17) and of methyl 4,6-O-benzylidene-3-O-(2,3:4,6-di-O-isopropylidene-alpha-D-mannopyranosy l)- alpha-D-glucopyranoside, an intermediate for the synthesis of 2-O-glycosyl-3-O-(alpha-D-mannopyranosyl)-D-glucoses.

Acetylation↗
PubMed1989

Synthesis of four structural elements of xylose-containing carbohydrate chains from N-glycoproteins.

The synthesis of the oligosaccharides beta-D-Xylp-(1----2)-beta-D-Manp-OMe (12), beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----6)]-beta-D-Manp+ ++-OMe (17), beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----3)]-beta-D-Manp+ ++-OMe (21), and beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----3)] [alpha-D-Manp-(1----6)]-beta-D-Manp-OMe (25) is described. Methyl 3-O-benzyl-4,6-O-isopropylidene-beta-D-mannopyranoside (6) was prepared from the corresponding glucoepimer (4) by oxidation, followed by stereoselective reduction. Condensation of 6 with 2,3,4-tri-O-acetyl-alpha-D-xylopyranosyl bromide in the presence of mercuric cyanide gave a 1:9 mixture of methyl 3-O-benzyl-4,6-O-isopropylidene-2-O-(2,3,4- tri-O-acetyl-alpha- (7a) and -beta-D-xylopyranosyl)-beta-D-mannopyranoside (7), and then 7 was converted into the acetylated disaccharide-glycoside 11. Regioselective mannosylation, with 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl bromide, at position 6 of deisopropylidenated 7 (8), using mercuric bromide as a promoter, afforded the trisaccharide-glycoside derivative 13, which was transformed into the acetylated trisaccharide-glycoside 16. The disaccharide derivative 10, obtained from 8, and the trisaccharide derivative 15, obtained from 13, were glycosylated at position 3 with O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)trichloroacetimidate (19), using trimethylsilyl triflate as a promoter, giving rise to acetylated tri- (20) and tetra-saccharide (24) derivatives, respectively. O-Deacetylation of 11, 16, 20, and 24 gave 12, 17, 21, and 25, respectively.

Carbohydrate Conformation↗
PubMed1988

Synthesis of the tetrasaccharide core region of antigenic lipo-oligosaccharides characteristic of Mycobacterium kansasii.

The oligosaccharide core region, beta-D-Glcp-(1----3)-beta-D-Glcp-(1----4)-alpha-D-Glcp- 1----1)-alpha-D-Glcp (1), of the lipo-oligosaccharide-type antigens isolated from M. kansasii has been synthesised from 2,3,2',3',4',6'-hexa-O-benzyl-6-O-(1-phenylethyl)-alpha, alpha-trehalose (4). Compound 4 was obtained by LiAlH4-AlCl3-type hydrogenolysis of 2,3,2',3',4',6'-hexa-O-benzyl-4,6-O-(S)-(1-phenylethylidene)-alpha , alpha-trehalose. The beta-laminaribiosyl part of the molecule was built-up by sequential glycosylation steps using 2,4,6-tri-O-acetyl-3-O-allyl-alpha-D-glucopyranosyl bromide in the presence of HgBr2 and methyl 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranoside promoted by methyl triflate. The complete a priori 13C-n.m.r. spectrum assignment of 1 was achieved by applying 2D methods.

Indicators and Reagents↗
PubMed1987

Glycosylated trehalose. Synthesis of the oligosaccharides of the glycolipid-type antigens from Mycobacterium smegmatis.

The oligosaccharide components, 3-O-Me-beta-D-Glcp-(1----3)-beta-D-Glcp-(1----4)-beta-D-Glcp-(1----6)- alpha-D-Glcp-(1----1)-alpha-D-Glcp (1) and beta-D-Glcp-(1----4)-beta-D-Glcp-(1----6)-alpha-D-Glcp-(1----1)-alpha-D- Glcp, of the glycolipid-type antigens isolated from M. smegmatis have been synthesised from 2,3,4,2',3',4',6'-hepta-O-acetyl-alpha,alpha-trehalose and the appropriate glycosyl bromides under Helferich conditions with Hg(CN)2 as the promoter. Condensation of the trisaccharide glycosyl bromide 27 gave an orthoester derivative (28) which could be rearranged, using HgBr2 or boron trifluoride etherate, into the acetylated derivative (29) of 1. The model compound beta-D-Glcp-(1----6)-alpha-D-Glcp-(1----1)-alpha-D-Glcp has also been synthesised.

Antigens, Bacterial↗
PubMed1986

Synthesis of the tetrasaccharide repeating-unit of the lipopolysaccharide isolated from Pseudomonas maltophilia.

The title tetrasaccharide having the structure 3-O-Me-beta-L-Xylp-(1----4)- alpha-L-Rhap-(1----4)-alpha-L-Rhap-(1----2)-L-Rhap was obtained by reaction of the alpha-acetobromo derivative of 4-O-(3-O-methyl-beta-L-xylopyranosyl)-L-rhamnopyranose and benzyl 3,4-di-O-benzyl-2-O-(2,3-O-isopropylidene-alpha-L-rhamnopyranosyl)- alpha-L-rhamnopyranoside, followed by removal of the protecting groups. The synthesised compounds were characterised on the basis of n.m.r. data.

Carbohydrate Sequence↗
PubMed1978

Structural investigation of the antibiotic ristomycin A. 13C-NMR spectral analysis of the interglycosidic linkages of the heterotetrasaccharide side-chain.

By 13C-NMR studies on Ia, IIa, IIb and IVa obtained by the chemical degradation of ristomycin A and on several synthetic model compounds it has been proved that an O-beta-D-arabinopyranosyl-(1 leads to 2)-O-alpha-D-mannopyranosyl-(1 leads to 2)-O-[alpha-L-rhamnopyranosyl-(1 leads to 6)]-D-glucopyranosyl heterotetrasaccharide moiety is connected to the aglycone of the antibiotic.

Chemical Phenomena↗
PubMed1976

Structural investigation of the antibiotic ristomycin A. Synthesis of ristobiose and ristotriose.

Proof is given by synthesis confirming the structure of ristobiose as 2-O-alpha-D-mannopyranosyl-D-glucose (IV) and ristotriose as O-alpha-L-rhamnopyranosyl (1 leads to 6)-O-[alpha-D-mannopyranosyl (1 leads to 2)]-D-glucose (X) which are obtained from ristomycin A upon mild acid hydrolysis. Both oligosaccharides, IV and X, have been detected for the first time as the components of an antibiotic.

Hydrolysis↗