Stereoselective glycosylation using fully benzylated pyrimidin-2-yl 1-thio-β-d-glycopyranosides (original) (raw)

1995, Carbohydrate Research

Pyrimidin-2-yl 2,3,4,6-tetra-O-benzyl-l-thio-fl-D-gluco-(5) and-/3-D-galacto-pyranoside (6), and pyrimidin-2-yl 2,3,4-triO -benzyl-l-thio-/3-D-xylo-(7), and-aD -arabino-pyranoside (8) were readily prepared from the corresponding per-O-acetylated 1-thioglycopyranosides, which were in turn obtained from the relevant acetobromosugars and 2-mercaptopyrimidine under phase-transfer conditions. Glycosidic coupling reactions using 5 (or 6, 7, or 8) as the donor and methyl 2,4,6-triO -benzyl-a-o-mannopyranoside as the acceptor in the presence of trimethylsilyl triflate afforded 1,2-cis-configured, 1 ~ 3-1inked disaccharides (a from 5, 6, and 7, fl from 8) as the sole products in moderate to excellent yields. The coupling reaction of 6 (or 7 or 8) with 1,2:3,4-di-Oisopropylidene-ot-D-galactopyranose in the presence of silver triflate furnished 1 ~ 6-1inked disaccharides in high yield, with the 1,2-cis isomers predominant.