Studies on the Inhibition of Mandelate Racemase by Arylboronic Acids

Abstract

Mandelate racemase (MR) is an enzyme that catalyzes the Mg2+-dependent interconversion of (R)- and (S)-mandelate, and has served as a model enzyme for exploring the limit of the available free energy of transition state (TS) stabilization (ΔGtx) that an inhibitor can capture. This work explored this limit by studying the inhibition of MR by various arylboronic acids, and found that phenylboronic acid (PBA)-based inhibitors were the most potent competitive inhibitors of MR. From a survey of various polysubstituted PBAs, 3,4-dichloro-PBA was found to be the most potent inhibitor of MR identified to date, and recognized by MR as an analogue of the TS. MR preferentially binds 3,4-dichloro-PBA in its sp3-hybridized form (Ki = 5.7 ± 0.5 nM), capturing ~45% of ΔGtx. This work highlights the value of the boronic acid group and halogen substitution in the design of potent enzyme inhibitors.