A Tricatecholic Receptor for Carbohydrate Recognition:  Synthesis and Binding Studies

A new tripodal receptor bearing three catechol subunits on a benzene platform has been synthesized in four steps from 1,3,5-triethylbenzene and pyrogallol. The binding ability of the tricatecholic receptor was investigated toward several monosaccharides in CDCl3, where multiple equilibria were detected, and compared to that of a previously reported trisureidic receptor of analogous structure. Association constants were measured by 1H NMR titrations, and the corresponding affinities were assessed through the BC50 parameter, a binding descriptor univocally defining the affinity of a host for a guest in multi-equilibrium systems. Results show that the tripodal catecholic receptor binds the octyl glycosides with affinities ranging from 0.87 to 5.2 mM and with a 6-fold selectivity factor for the alpha-mannoside over the beta-glucoside. Although the affinity for glycosides was not appreciably improved with respect to the ureidic receptor, a significant change in selectivity was obtained by the H-bonding group replacement.