ɑ-Amino acids have been used in combination with NaBH4 for the asymmetric reduction of ketones. Of a number of amino acids the sterically hindered tert-leucine was found to give the highest ee (95%) in the reduction of the carbonyl group of a 1,5-benzothiazepine intermediate in an efficient synthesis of the calcium antagonist diltiazem: J. Org. Chem., 61, 8586 (1996).