Byline: Chun-Sheng Chang (1), Ssu-Ching Ho (1) Keywords: Carica papaya lipase; Enantioselective esterification; 2-methylalkanoic acid; Water activity Abstract: Isooctane was the best reaction medium for the enantioselective esterification of (R,S)-2-methylalkanoic acid with n-butanol using Carica papaya lipase as catalyst. Increasing linear alkyl-chain length of racemic 2-methylalkanoic acids from ethyl to hexyl increased the enantioselectivity (E) from 2.1 to 98.2 for the esterification of racemic 2-methylalkanoic acids with n-butanol at 35degC. Decreasing reaction temperature from 40 to 20degC increased the enantioselectivity (E) from 14 to 33 for the esterification of racemic 2-methylhexanoic acids with n-butanol. We obtained a maximum enantioselectivity, of E = 24.3, for the enantioselective esterification of racemic 2-methylhexanoic acids with n-butanol in isooctane at water activity 0.33, and at 35degC. Author Affiliation: (1) Department of Biotechnology, Southern Taiwan University, Tainan, 710, Taiwan Article History: Registration Date: 02/07/2011 Received Date: 07/05/2011 Accepted Date: 01/07/2011 Online Date: 10/07/2011 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s10529-011-0692-7) contains supplementary material, which is available to authorized users.