Secondary amides of (R)-3,3,3-trifluoro-2-hydroxy-2-methylpropionic acid as inhibitors of pyruvate dehydrogenase kinase

N'-Methyl-N-(4-tert-butyl-1,2,5,6-tetrahydropyridine)thiourea, SDZ048-619 (1), is a modest inhibitor (IC50 = 180 mu M) of pyruvate dehydrogenase kinase (PDHK). in an optimization of the N-methylcarbothioamide moiety of 1, it was discovered that amides with a small acyl group, in particular appropriately substituted amides of (R)-3,3,3-trifluoro-2-hydroxy-2-methylpropionic acid, are inhibitors of PDHK. Utilizing this acyl moiety, herein is reported the rationale leading to the optimization of a series of acylated piperazine derivatives. Methyl substitution of the piperazine at the 2- and 5-positions (with S and R absolute stereochemistry) markedly increased the potency of the lead compound (> 1000-fold). Oral bioavailability of the compounds in this series is good and is optimal (as measured by AUC) when the 4-position of the piperazine is substituted with an electron-poor benzoyl moiety. (+)-1-N-[2,5-(S,R)-Dimethyl-4-N-(4-cyanoben-zoyl)piperazine]-(R)-3,3,3-trifluoro-2-hydroxy-2-methylpropanamide (14e) inhibits PDHK in the primary enzymatic assay with an IC50 of 16 +/- 2 nM, enhances the oxidation of [C-14]lactate into (CO2)-C-14 in human fibroblasts with an EC50 of 57 +/- 13 nhl, diminishes lactate significantly 2.5 h post-oral-dose at doses as low as 1 mu mol/kg, and increases the ex vivo activity of PDH in muscle, liver, and fat tissues in normal Sprague-Dawley rats. These PDHK inhibitors, however, do not lower glucose in diabetic animal models.