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PubMed1993

Recognition of synthetic deoxy and deoxyfluoro analogs of the acceptor alpha-L-Fuc p-(1-->2)-beta-D-Gal p-OR by the blood-group A and B gene-specified glycosyltransferases.

The disaccharide alpha-L-Fuc p-(1-->2)-beta-D-Gal p-O-(CH2)7CH3 (6), is an acceptor for both glycosyltransferases responsible for the biosynthesis of the A and B blood-group antigens. These enzymes transfer GalNAc and Gal, respectively, with an alpha-linkage to OH-3 of the Gal residue in 6. All six possible deoxy and deoxyfluoro analogs of 6, with modifications on the target Gal residue, were chemically synthesized and kinetically evaluated as both substrates and inhibitors for the A and B glycosyltransferases. Both enzymes will tolerate replacement of the hydroxyl groups at the 3 and 6 positions of the Gal residue. Substitution of OH-4 of the Gal residue, however, abolishes recognition by these glycosyltransferases. The 6-deoxy and 6-fluoro compounds are substrates for both enzymes while the 3-deoxy and 3-fluoro compounds are competitive inhibitors, with Ki values in the range 14-110 microM. Kinetic constants have been determined for the 6-deoxy and 6-fluoro derivatives.

ABO Blood-Group System↗
PubMed1993

A new method of anomeric protection and activation based on the conversion of glycosyl azides into glycosyl fluorides.

Glycosyl azides provide reliable anomeric protection stable to conditions for hydrolytic removal of ester groups, for reductive opening or release of acetalic diol protection, for the introduction of ether-type protection, and for glycosylation processes. The utility of this anomeric protection is further enhanced as glycosyl azides may be converted into glycosyl fluorides, which can be activated for glycosylation reactions. To this end, glycosyl azides have been subjected to 1,3-dipolar cycloaddition with di-tert-butyl acetylenedicarboxylate. On treatment with hydrogen fluoride-pyridine complex the N-glycosyl triazole derivatives directly give glycosyl fluorides.

Azides↗
PubMed1993

Synthesis of 4-nitrophenyl O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)- (1-->2)-O-(6-O-methyl-alpha-D-mannopyranosyl)-(1-->6)-beta-D- glucopyranoside and its 4',6'-di-O-methyl analog. Potential inhibitors of N-acetylglucosaminyl-transferase V (GnT-V).

O-(2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-(1-->2) -3,4 - di-O-acetyl-6-O-methyl-alpha-D-mannopyranosyl bromide and O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)- (1-->2)-3-O-acetyl-4,6-di-O-methyl-alpha-D-mannopyranosyl bromide were each condensed with 4-nitrophenyl 2,3-di-O-acetyl-beta-D-glucopyranoside, and the products were deprotected to yield, respectively, beta-D-Glc p NAc-(1-->2)-6-O-Me-alpha-D-Man p-(1-->6)-beta-D-Glc p and beta-D-Glc p NAc-(1-->2)-4,6-di-O-Me-alpha-D-Man p-(1-->6)-beta-D-Glc p, as their 4-nitrophenyl glycosides. These trisaccharides are expected to function as inhibitors for N-acetylglucosaminyltransferase V.

Carbohydrate Conformation↗
PubMed1993

Synthesis of sulfated glucuronyl glycosphingolipids; carbohydrate epitopes of neural cell-adhesion molecules.

The sulfated glucuronyl glycosphingolipids isolated from the human peripheral nervous system, HO3S-3-beta-GlcpA-(1-->3)-[beta-D-Galp-(1-->4)-beta-D-GlcpNA c-(1-->3)]n- beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->1)-Cer (n = 1, 2) (1 and 2) were synthesized. The glycan part of target molecules was designed to be constructed from glucuronate, lactosamine, and lactose fragments 8, 9 (or 10), and 11, which in turn were synthesized stereo- and/or regio-selectively from readily available compounds. The coupling reaction between 9 and 11 was performed by the action of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf)), and subsequent manipulation of product 31 gave 33. On the other hand, slight modification of this sequence, including repetitive glycosylation reactions using 10, afforded hexasaccharide 46. These compounds were reacted with nonreducing end glucuronate synthon 8 under the agency of CuBr2-AgOTf-Bu4NBr, and the resultant penta- and hepta-saccharides 34 and 47, respectively, were transformed into glycosyl fluorides. Final coupling with the ceramide derivative 7, followed by chemoselective deprotection of the levulinoyl group, sulfation and complete deprotection, afforded the target glycolipids 1 and 2.

Carbohydrate Conformation↗
PubMed1993

Syntheses of nephritogenoside and related compounds.

Nephritogenoside has been prepared by coupling of the acyl azide derivative of a N-triglycosyl dipeptide, derived from the corresponding hydrazide derivative of O-(2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl)-(1-->6)-O-(2,3,4-tri-O -acetyl - beta-D-glucopyranosyl)-(1-->6)-2,3-di-O-benzyl-1-N-[N-(tert-butoxycarbon yl)- L-aspart-1-oyl-(L-proline methyl ester)-4-oyl]-alpha-D-glucopyranosylamine, with a nonadecapeptide, followed by deprotection of the desired protected nephritogenoside. The N-triglycosyl pentapeptide also has been prepared as a model compound.

Amino Acid Sequence↗
PubMed1993

Synthesis of a terminal A-B-C disaccharide fragment of flambamycin, curamycin, and avilamycin.

Methyl 2,6-dideoxy-4-O-[2,6-dideoxy-4-O-(3,5-dichloro-4-hydroxy-2-methoxy-6- methylbenzoyl)-beta-D-arabino-hexopyranosyl]-alpha-D-arabino-he xopyranoside (25) corresponds to an A-B-C disaccharide subunit of the title antibiotics. It was synthesized from suitably protected monosaccharide and aromatic precursors. The readily available 4,6-O-benzylidene-1,2-O-(R)-propylidene-alpha-D-glucopyranose was converted in six steps into 2-O-acetyl-4-O-benzoyl-3-O-benzyl-6-deoxy-alpha-D-glucopyranosyl bromide, which was condensed with methyl 3-O-benzyl-2,6-dideoxy-alpha-D-arabino-hexopyranoside in the presence of mercury(II) cyanide. Methyl 4-O-(2-O-acetyl-4-O-benzoyl-3-O-benzyl-6-deoxy-beta- D-glucopyranosyl)-3-O-benzyl-2,6-dideoxy-alpha-D-arabino-hexopyranosi de was converted either into methyl 2,6-dideoxy-4-O-(6-deoxy-beta-D- glucopyranosyl)-alpha-D-arabino-hexopyranoside by removal of the protective groups or into methyl 3-O-benzyl-4-O-(3-O-benzyl-2,6-dideoxy-beta-D-arabino-hexopyranosyl)-2,6 - dideoxy-alpha-D-arabino-hexopyranoside (22) by selective deacetylation, Barton deoxygenation, and Zemplén debenzoylation. Disaccharide 22 was deprotonated with butyllithium and treated with 4-benzyloxy-3,5-dichloro-2-methoxy-6-methylbenzoyl chloride to give the title compound 25 after hydrogenolysis.

Anti-Bacterial Agents↗
PubMed1993

Enzymatic synthesis of some O-beta-D-digalactosyl glycopeptides, using beta-D-galactosidase.

Disaccharide-peptide conjugates were obtained in yields of 30-50% from o-nitrophenyl beta-D-galactopyranoside by employing beta-D-galactosidase from E. coli as catalyst. Two series of beta-D-galactosyldipeptides were examined as galactosyl acceptors. They both contain an L-serine residue beta-linked to the anomeric carbon of galactose. In the first series, serine is in the N-terminal position of the dipeptide; in the second series, serine is in the C-terminal position. The second amino acid is L-alanine or glycine. Some of our substrates gave a high yield of beta-(1-->3)-digalactosyldipeptide derivatives and all gave very little of the beta-(1-->6) regioisomer. The conditions and the limitations of the transgalactosylation reaction are discussed.

Carbohydrate Conformation↗
PubMed1993

Microscopic protonation constants in tobramycin. An NMR and pH study with the aid of partially N-acetylated derivatives.

Three tetra-N-acetyl derivatives and one tri-N-acetyl derivative of tobramycin (1) have been prepared by partial N-acetylation. Comparison of the pKa values, determined by NMR chemical shift titrations and pH titration of the derivatives, with those of unprotected 1 suggests that protonation equilibria at any particular amino group in 1 are not likely to be influenced by those at other sites. pH-Dependent conformational changes in 1 were assessed on the basis of 1H and 13C chemical shift changes in the derivatives.

Acetylation↗
PubMed1993

A convenient synthesis of N-acetyllactosamine derivatives from lactal.

In a thermal inverse-type hetero-Diels-Alder reaction of O-silyl-protected lactal 1 and bis(2,2,2-trichloroethyl) azodicarboxylate (2), the dihydrooxadiazine derivative 3 was obtained in a very high yield; transesterification with benzyl alcohol furnished the corresponding derivative 4. Treatment of 3 with methanol in the presence of BF3.OEt2 afforded the methyl lactoside derivative 5 which, after transesterification with benzyl alcohol, then hydrogenolytic debenzylation and concomitant NN-cleavage with Raney nickel, and N-acetylation, furnished methyl O-(2,4,6-tri-O-tert-butyldimethylsilyl-beta-D-galactopyranosyl)-(1-->4)- 2-acetamido-3,6-di-O-tert-butyldimethylsilyl-2-deoxy-beta-D-glucopyra nos ide (7) in high yield. Desilylation of 4, then O-acetylation, methyl glycoside formation with methanol-BF3.OEt2, hydrogenolytic debenzylation, and NN-cleavage with Raney nickel, and N-acylation afforded methyl O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->4)-2-acetamido-3 ,6-di-O-acetyl-2-deoxy-beta-D-glucopyranoside (10).

Amino Sugars↗
PubMed1993

Characterization of inhibitory activities and binding mode of synthetic 6'-modified methyl N-acetyl-beta-lactosaminide toward rat liver CMP-D-Neu5Ac: D-galactoside-(2-->6)-alpha-D-sialyltransferase.

6'-Deoxy (12), 6'-thio (13), and 6'-O-tetrahydropyranosyl (14) analogues of methyl N-acetyl-beta-lactosaminide (3), were synthesized from lactose. NOE experiments proved that they adopt the same conformation as that of 3. Inhibition studies using these synthetic analogues, including the disulfide dimer 15, toward (2-->6)-alpha-sialytransferase (EC 2.4.99.1) revealed that the 6'-deoxy analogue 12 had remarkable inhibitory activity as the first acceptor-analogue inhibitor for this enzyme. It is noteworthy that the disulfide 15 also behaves as an inhibitor. The results indicated that chemical modification at the 6'-position of 3 did not cause much decrease in the binding affinity to the sialytransferase. Further, a novel possibility that the acceptor and the acceptor-analogue inhibitor can bind simultaneously to the sialytransferase was proposed based on the inhibition studies with 12 and CMP.

Amino Sugars↗
PubMed1993

Synthesis of chlorodeoxy trisaccharides related to the Shigella flexneri Y polysaccharide.

Chloromethoxylation of di-O-acetyl-L-rhamnal has been employed as a convenient route to methyl 3,4-di-O-acetyl-2-chloro-2-deoxy-alpha-L-rhamnopyranoside 7, which was converted into an ethyl thioglycoside 10, suitable for use as a glycosyl donor. It and a disaccharide analogue 20 were effective donors in N-iodosuccinimide-triflic acid promoted glycosylations of a 2-acetamido-2-deoxy-D-glucopyranoside acceptor 22. Chlorodeoxy saccharides have previously been shown to be suitable derivatives to probe oligosaccharide-protein interactions, and this synthetic strategy provided three monochlorodeoxy trisaccharide congeners of the native Shigella flexneri epitope 2, alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->3)-beta-D-GlcNAcp+ ++-(1-->O)-Me.

Carbohydrate Conformation↗
PubMed1993

"Fast moving" and "slow moving" heparins, dermatan sulfate, and chondroitin sulfate: qualitative and quantitative analysis by agarose-gel electrophoresis.

Heparin from beef intestinal mucosa, dermatan sulfate from beef intestinal mucosa, and chondroitin sulfate from bovine trachea were extracted and purified, and their structures and physico-chemical properties were evaluated by different techniques (disaccharide patterns by specific enzymatic cleavage, relative molecular mass by high-performance size-exclusion chromatography, sulfate-to-carboxyl ratio by potentiometric determination). Heparin was fractionated into "slow moving" and "fast moving" fractions by selective precipitation as the barium salt at different temperatures. The "fast moving" and "slow moving" components of heparin, dermatan sulfate, and chondroitin sulfate were utilized to run calibration curves in agarose-gel electrophoresis. Mixtures containing different amounts of these glycosaminoglycans were made and separated by agarose-gel electrophoresis, and these were analyzed quantitatively. For analysis of relative amounts, the area of each individual component of mixtures, obtained by photodensitometric readings, was divided by the sum of the areas of all glycosaminoglycans and expressed as a percentage. For analysis of absolute amounts, the area under the curve for each component of mixtures was fitted to specific calibration curves, and the amount of each glycosaminoglycan was calculated in micrograms. The quantitative procedure performed by analysing absolute amounts was used to obtain an accurate quantitative evaluation of each component in mixtures of glycosaminoglycans utilized for pharmaceutical purposes. A sensitive method was developed for the evaluation of very small amounts (0.2% w/w) of possible glycosaminoglycans as contaminants in preparations of a single species of glycosaminoglycan. This technique requires specific enzymatic degradation by bacterial lyases, separation in agarose-gel electrophoresis, and quantitative analysis by photodensitometric analysis and specific calibration curves.

Animals↗