The Candida antarctica lipase A-catalysed N-acylation of ethyl 3-amino-2-ethylpropanoate rac-3 and methyl 3-amino-2-isopropylpropanoate rac-6 was performed with ethyl butanoate in tert-amyl alcohol at 4 degrees C. The resulting enantiomerically enriched derivatives were isolated as N-Boc-protected amino esters (R)-9 and (R)-10 and butyramides (S)-7 and (S)-8 (ee: 76-95%). (C) 2008 Elsevier Ltd. All rights reserved.