(S)-CPP is an inhibitor of branched-chain α-ketoacid dehydrogenase complex (BCKDC) kinase, also know as BDK, or keto acid dehydrogenase kinase. BDK is a negative regulator of BCKDC activity. Inhibition of BDK by (S)-CPP (IC50 = 6.3 µM) leads to complex activation, and significant reduction of plasma levels of leucine/isoleucine and valine in wild type mice.