Lanthanum-catalyzed aqueous acylation of monosaccharides by benzoyl methyl phosphate

Abstract

It was previously reported that diols dissolved in water (pH 8, EPPS buffer) react with benzoyl methyl phosphate (BMP) in the presence of lanthanide ions to form monobenzoyl esters. We have investigated the possibility of extending this process to include formation of esters of monosaccharides in water from lanthanide-catalyzed reactions with BMP. The combination of methyl-α-D-glucopyranoside and BMP in the presence of lanthanum trichloride gave selective monoacylation of the 2- and 6-hydroxyl groups in a ratio of 2:1. The likely mechanism involves preferential bisbidentate coordination of BMP and the diol to lanthanide ion (which explains how an ester forms when water is in enormous excess) followed by base-catalyzed intramolecular acyl transfer. The method should be generally applicable where a selective acylation reaction in water as solvent is desirable. Key words: benzoyl methyl phosphate, lanthanide, catalysis, water, monoacylation, selective.