Synthesis of α-d-galactopyranosyl-linked oligosaccharides having an anomeric 4-nitrophenyl group by the use of a 2,6-di-O-(4-methoxybenzyl) derivative of d-galactose as a donor

✍ Scribed by Rakesh K. Jain; Arun K. Sarkar; Khushi L. Matta

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 294 KB
• Volume: 220
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(91)80023-g

✦ Synopsis

Among the various reagents developed for a-glycosylation of D-glucose, Dgalactose, and L-fucose', practically all of them possess a 20benzyl group as a nonparticipating protecting group, which necessitates hydrogenolysis for its removal. As a result, the synthesis of oligosaccharides containing either 4nitrophenyl or benzyl anomeric groups is not practical. There is a need for such 4nitrophenyl or benzyl glycosides of oligosaccharides for rapid assays of glycosyltransferases and glycosidases. Moreover, these 4-nitrophenyl glycosides become unique chromogenic substrates for a search of endoglycosidases. Recently, we reported3 the use of methyl 3,4-O-isopropylidene-2-O-(4-methoxybenzyl)-l-thio-~-L-fucopyranoside as a glycosylating reagent for the synthesis of a+fucosylated oligosaccharides containing 4-nitrophenyl and benzyl aglycons. We report herein the use of a 2,6-di-O-(4-methoxybenzyl)derivative of Dgalactose in similar synthesis.

Methyl 3,4-O-isopropylidene-2,6-di-O-(4-methoxybenzyl)-l-thio-P-D-galactopyranoside (3) was prepared in four steps from 1,2,3,4,6-penta-O-acetyl+D-galactopyranose. Treatment of this peracetate with (methylthio)trimethylsilane and trimethylsilyl triflate in dichloromethane produced a high yield (86%) of known methyl 2,3,4,6-tetra-O-acetyl-1 -thio-j?-D-galactopyranoside4 (1). 0-Deacetylation of 1 with methanolic sodium methoxide, followed with acetonation by the procedure of Catelani et al.', afforded known methyl 3,4-O-isopropylidene-1-thio-P-D-galactopyranoside4

(2) in 70% yield. Alkylation of 2 with sodium hydride and 4-methoxybenzyl chloride in N,N-dimethylformamide gave methyl 3,4-O-isopropylidene-2,6-di-O-(4-methoxybenzyl)-l-thio-P-ogalactopyranoside (3) in 78.6% yield after silica gel column chromatography,