A novel light-gated sugar receptor, which shows high glucose selectivity

Abstract

A bis(boronic acid)-based saccharide receptor (1) bearing a photoresponsive azobenzene moiety has been synthesised, aiming at the photocontrol of the saccharide-binding properties by the distance change between the two boronic acids. trans-1 is wholly CD-silent in the presence of various saccharides whereas cis-1 yielded CD-active species with D-glucose and D-allose in aqueous pH 10.5 solution and with D-glucose in methanol. The findings indicate that the two boronic acids in cis-1 can act cooperatively to selectively recognise these saccharides by the formation of the cyclic 1∶1 complexes. cis-to-trans thermal isomerisation slowly takes place in methanol (k_o = 2.1 × 10^–6 s^–1) but the rate is extremely slow in aqueous pH 10.5 solution (half-life 8.7 days). In methanol the rate is retarded only by D-glucose which forms a macrocyclic 1∶1 complex with cis-1. In aqueous pH 10.5 solution the cis-to-trans isomerisation could be induced virtually only by visible-light irradiation, indicating that this system is useful as a light-gated saccharide receptor.