LIPASE-MEDIATED RESOLUTION OF GAMMA-BRANCHED CHAIN FATTY-ACID METHYL-ESTERS

Kinetic resolution of the branched chain fatty acid (BCFA) esters 4-me thylhexanoic acid methyl ester (4) and 4-methyloctanoic acid methyl es ter (5) was investigated using a series of hydrolases as catalysts. In the transesterification of these methyl esters to their butyl esters, two enzymes showed good conversion and a moderate enantiomeric ratio (E). In the transesterification of 4, an E of 2 was obtained for the r eaction catalysed by Rhizomucor miehei lipase, whereas Candida antarct ica lipase B (CALB) showed an E of 5. In the conversion of 5 to the bu tyl ester, Rhizomucor il miehei lipase was unselective whereas CALB ga ve an E of 8. Apparently, changing from an ethyl group to a butyl grou p at the chiral centre leads to an improved chiral recognition by CALB . The lipases displayed complementary enantiomeric preference. Rhizomu cor miehei lipase favours the S-enantiomer of 4 while CALB preferentia lly transforms the R-enantiomer of both substrates. Molecular modellin g studies supported the measured stereochemical preference of CALB. A decrease in reaction temperature from 45 degrees C to 27 degrees C led to a significant increase in enantiomeric ratio (E = 23) in the trans esterification of 5. These results offer good perspectives for the pro duction of enantiomerically pure branched chain fatty acids.