α-Selective Glucosylation Can Be Achieved with 6-O-para-Nitrobenzoyl Protection.

A systematic study of the effect of various 6-O-acyl groups on anomeric selectivity in glucosylations with thioglycoside donors was conducted. All eight different esters were found to induce moderate-to-high α-selectivity in glucosylation with l-menthol with the best being 6-O-p-nitrobenzoyl. The effect appears to be general across various glucosyl acceptors, glucosyl donor types, and modes of activation. No evidence was found in favor of distal participation.

Anomeric Thioglycosides Give Different Anomeric Product Distributions under NIS/TfOH Activation.

The reaction of a series of anomeric thioglycosides with various glycosyl acceptors and N-iodosuccinimide/catalytic triflic acid was investigated with respect to reactivity and anomeric selectivity. In general, ß-configured donors were found to give a more ß-selective reaction outcome compared to their α-configured counterparts. The relative reactivity of various thioglycosides was measured through competition experiments, and the following order was established: phenyl, tolyl, methyl, ethyl, isopropyl, and 1-adamantyl.

Solvent free, catalytic and diastereoselective preparation of aryl and alkyl thioglycosides as key components for oligosaccharide synthesis.

A new and environmentally friendly protocol for the conversion of sugar per-acetates into thioglycosides under solvent free and catalytic conditions is presented. The procedure involves heating in the presence of InCl3 and various aryl thiols. For alkyl thioglycoside synthesis, cyclohexane thiol was found to give good results and yield a glycosyl donor with reactivity similar to a thioethyl congener. The established optimum reaction conditions were found to provide the desired thioglycoside products in an easy and highly diastereoselective manner even when conducted on a multigram scale.