The Discovery of in Vivo Active Mitochondrial Branched-Chain Aminotransferase (BCATm) Inhibitors by Hybridizing Fragment and HTS Hits

The hybridization of hits, identified by complementary fragment and high throughput screens, enabled the discovery of the first series of potent inhibitors of mitochondrial branched-chain aminotransferase (BCATm) based on a 2-benzylamino-pyrazolo­[1,5-<i>a</i>]­pyrimidinone-3-carbonitrile template. Structure-guided growth enabled rapid optimization of potency with maintenance of ligand efficiency, while the focus on physicochemical properties delivered compounds with excellent pharmacokinetic exposure that enabled a proof of concept experiment in mice. Oral administration of 2-((4-chloro-2,6-difluorobenzyl)­amino)-7-oxo-5-propyl-4,7-dihydropyrazolo­[1,5-<i>a</i>]­pyrimidine-3-carbonitrile <b>61</b> significantly raised the circulating levels of the branched-chain amino acids leucine, isoleucine, and valine in this acute study