α-Methylation enhances the potency of isoprenoid triazole bisphosphonates as geranylgeranyl diphosphate synthase inhibitors

Disruption of protein geranylgeranylation via inhibition of geranylgeranyl diphosphate synthase (GGDPS) represents a novel therapeutic strategy for a variety of malignancies, especially those characterized by excessive protein secretion such as multiple myeloma. Our work has demonstrated that some isoprenoid triazole bisphosphonates are potent and selective inhibitors of GGDPS. Here we present the synthesis and biological evaluation of a new series of isoprenoid triazoles modified by incorporation of a methyl group at the α-carbon. These studies reveal that incorporation of an α-methyl substituent enhances the potency of these compounds as GGDPS inhibitors, and, in the case of the homogeranyl/homoneryl series, abrogates the effects of olefin stereochemistry on inhibitory activity. The incorporation of the methyl group allowed preparation of a POM-prodrug, which displayed a 10-fold increase in cellular activity compared to the corresponding salt. These studies form the basis for future preclinical studies investigating the anti-myeloma activity of these novel α-methyl triazole bisphosphonates.