Synthesis and Biological Evaluation of Thiol-Based Inhibitors of Glutamate Carboxypeptidase II:  Discovery of an Orally Active GCP II Inhibitor

A series of 2-(thioalkyl)pentanedioic acids were synthesized and evaluated as inhibitors of glutamate carboxypeptidase II (GCP II, EC 3.4.17.21). The inhibitory potency of these thiol-based compounds against GCP II was found to be dependent on the number of methylene units between the thiol group and pentanedioic acid. A comparison of the SAR of the thiol-based inhibitors to that of the phosphonate-based inhibitors provides insight into the role of each of the two zinc-binding groups in GCP II inhibition. The most potent thiol-based inhibitor, 2-(3-mercaptopropyl)pentanedioic acid (IC50 = 90 nM), was found to be orally bioavailable in rats and exhibited efficacy in an animal model of neuropathic pain following oral administration.