Candida rugosa lipase as an enantioselective catalyst in the esterification of methyl branched carboxylic acids: resolution of rac-3,7-dimethyl-6-octenoic acid (citronellic acid)

Some chiral methyl branched alkanoic and alkenoic acids were used as substr ates in esterifications with 1-hexadecanol in cyclohexane at water activity a(w)=0.8 catalysed by immobilised Candida rugosa lipase (CRL). Citronellic acid was one of several chiral 2- and 3-methyl branched acids that were su ccessfully resolved by the catalyst. With 3-methyl-branched substrates the R-enantiomers reacted fastest; whereas with 2-methyl acids the lipase gener ally displayed S-preference except in one case where it displayed R-prefere nce. When a double bond was present in the chain, the selectivity of CRL (E =24-51) was greater compared with the corresponding saturated acid (E=17-23 ). Attempted transesterifications of vinyl acetate with some chiral 2- or 3 -methyl branched primary alcohols using crude CRL gave very low E-values (E =1-2). (C) 1999 Elsevier Science Ltd. All rights reserved.