6-O-benzyl- and 6-O-silyl-N-acetyl-2-amino-2-N,3-O-carbonyl-2- deoxyglucosides: Effective glycosyl acceptors in the glucosamine 4-OH series. Effect of anomeric stereochemistry on the removal of the oxazolidinone group

Abstract

(Chemical Equation Presented) The 4-OH groups of both α- and β-methyl glycosides of N-acetylglucosamine, protected with an oxazolidinone spanning the nitrogen and O-3, and bearing benzyl or silyl protection on O-6, show excellent reactivity as acceptors in couplings to a range of glycosyl donors. The enhanced reactivity of these acceptors is attributed in part to the tied back nature of the oxazolidinone, which reduces hindrance around the nucleophilic oxygen. The N-acetyloxazolidinone function also reduces the tendency seen in simple N-acetylglucosamines toward amide glycosylation, and removes the possibility of problematic hydrogen bonding networks. In the β-, but not the α-, series selective hydrolysis of the N-acetyloxazolidinone directly to the N-acetylglucosamine was possible with barium hydroxide, a feature attributed to chelate formation between the acetamide carbonyl group and the glycosidic oxygen in the β-series.