Elaboration on the access to (S)-4-(4-methylbenzyl)oxy-3-hydroxybutanenitrile, a key intermediate for statins, by combining the kinetic resolution of racemate and the recycle of undesired enantiomer

High enantioselectivity (E 94) was observed in Candida antarctica lipase B-catalyzed hydrolysis of the corresponding acetate of racemic title compound. The reaction rate of the slow (S)-isomer was effectively suppressed by lowering the reaction temperature from 25 °C to 5 °C, to allow a five times increase of the enantioselectivity. The ee of the (S)-isomer, reached 97.8% at the reasonable conversion (52%) as the unreacted recovery, and the repetition of the enzymatic reaction provided pure enantiomer. The undesired (R)-isomer was oxidized with IBX and reduced with whole-cell biocatalysis with Candida floricola JCM 9439 to (S)-isomer (63.2% ee), which serves as the enantiomerically enriched substrate for further lipase-catalyzed resolution. The combination of total processes provided over 50% yield of the pure (S)-isomer, exceeding the theoretical limit for the enantiomeric resolution of racemate.