Photoswitch inhibitors of alpha-chymotrypsin--increased substitution and peptidic character in peptidomimetic boronate esters

A series of peptidomimetic boronate esters containing the photoisomerisable azobenzene group has been synthesised and assayed against the serine protease alpha-chymotrypsin. Compounds with borophenylalanine inhibition groups were found to be inhibitors with micromolar activity, while those with aryl boronate inhibition groups were inactive. Selected compounds were isomerised by UV or visible light to obtain enriched states of the (Z) or (E) isomers, respectively, and assayed. A change in activity on photoisomerisation was observed, however some decomposition of the boronate group on irradiation was also observed, limiting reversibility.