Abstract
New functionalized DMAPs having carboxylic acid functionality are developed for regioselective acylation of carbohydrates. In these catalysts, DMAP (4-( N, N-dimethylamino)pyridine) is linked with –COOH (–COOMe or –OSO 3H in reference catalysts) via methylene spacers of different length at the dimethylamino moiety. Utilizing one of these catalysts, 3-[ N-decyl- N-(4-pyridyl)amino]propionic acid ( 1 ), regioselectivity for the primary 6-OH group in acetylation of 1- O-octyl β- d-glucopyranoside is increased from 16% to 89% with rather improved catalytic activity compared with the parent DMAP. Catalyst 1 regioselectively acetylates both anomers of 1- O-octyl glucopyranosides (89% and 88% regioselectivity for β- and α-anomer, respectively) and 1- O-octyl galactopyranosides (100% regioselectivity for both anomers) at position 6 in CHCl 3, but gives nearly 1:1 mixtures of 4- and 6-monoacetates in the case of 1- O-octyl mannopyranosides. Control experiments are done to investigate the mechanistic aspects of regiocontrol.
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