Influence of the position of the substituent on the efficiency of lipase-mediated resolutions of 3-aryl alkanoic acids

Hydrolase-catalysed kinetic resolutions to provide enantioenriched a-substituted 3-aryl alkanoic acids are described. (S)-2-Methyl-3-phenylpropanoic acid (S)-1a was prepared in 96% ee by Pseudomonas fluorescens catalyzed ester hydrolysis, while, Candida antarctica lipase B (immob) resolved the a-ethyl substituted 3-arylalkanoic acid (R)-1b in 82% ee.
The influence of the position of the substituent relative to the ester site on the efficiency and enantioselectivity of the biotransformation is also explored; the same lipases were found to resolve both the a- and b-substituted alkanoic acids. Furthermore, the steric effect of substituents at the C2 stereogenic center relative to that for their C3 substituted counterparts on the efficiency and stereoselectivity is discussed.