Selectivity of Candida antarctica B Lipase toward Fatty Acid and (Iso)propanol Substrates in Esterification Reactions in Organic Media

Fatty acid (FA) selectivity of immobilized Candida antarctica B lipase was assessed as influenced by various cosubstrate systems for ester synthesis. Reaction mixtures contained a homologous series of even-chain n-acyl donor (C4 - 16) substrates (FA or their methyl esters, FAME) and a single alcohol cosubstrate (propanol, 2-propanol, or their acetate derivatives) in hexane. Multiple FA optima were often observed, with preferences for C6 (or C4) followed by C14 and sometimes C10. The degree of selectivity among acyl donors was modest (up to 1.28−2.60, based on ratios of selectivity constants) and was dependent on the choice of cosubstrate system. Acyl group selectivity ranged up to 1.31−1.36 for [FA + alcohol], 1.48−2.60 for [FAME + alcohol], 1.30−1.72 for [FA + alcohol acetate], and 1.28−1.88 [FAME + alcohol acetate] reaction systems. General shifts in selectivity were observed between short-chain (C4 - 8) and long-chain (C10 - 16) FA as groups with propanol cosubstrate, whereas shifts in reaction selectivity were observed toward specific FA(s) for 2-propanol cosubstrate. Selectivity among a series of alcohol cosubstrates ranged up to 13-fold in esterification reactions with C6 FA. Keywords: Lipase; anhydrous; selectivity; ester modification; Candida antarctica