Host-guest complexation-37 : Synthesis and binding properties of a transacylase partial mimic with imidazole and benzyl alcohol in place

Abstract

The design and 30-step synthesis of a transacylase partial mimic is described. The target catalyst combines a macrocyclic binding site, a hydroxymethyl group, and an imidazole group organized to act cooperatively through their attachment to a quaterphenyl support structure. The binding site is composed of three cyclic urea units in a tripod arrangement, rigidified by their incorporation into a macrocycle along with two anisyl and one m-xylyl spacer units. The binding and catalytic sites are complementary to amino acid ester salts. The host catalyst collects and orients through complexation the guest substrate to provide substantial rate enhancements for transacylation of amino ester salts. The free energies are reported for the host in CDCl3 binding the picrate salts of Li+, Na+, K+, Rb+,Cs+, NH4+, CH3NH3+ and t-BuNH3+.