Synthesis of Thiourea-Linked Glycooligomers that Mimic the Branching Patterns of Natural Oligosaccharides

Abstract

A general blockwise strategy for the synthesis of accurately sequenced unnatural glycooligomers that can reproduce the branching patterns encountered in native oligosaccharides, based on the use of thiourea groups as intersaccharide bridges, is reported. The linear pseudooligosaccharide backbone is built from monosaccharide building blocks bearing a latent amino group and an isothiocyanate functionality through an iterative process in three steps per cycle that include: (i) thiourea-forming reaction, (ii) deprotection of the hydroxyl groups in the adduct and (iii) generation of a new amino group in the growing chain. Branching points are incorporated by inserting links bearing orthogonal amine functionalities at specific locations in the chain. The approach is illustrated by the preparation of glucopyranosylthiourea pseudoheptasaccharides that mimic the branching patterns of a phytoalexin elicitor oligosaccharine and of lentinan.