Deracemization of secondary alcohols by chemo-enzymatic sequence with plant cells

Abstract

A screening based on undifferentiated plant cells allowed identifying Gardenia jasminoides as the best biocatalyst to perform the kinetic resolution of 1-phenylethanol. This species was further tested for its ability to oxidize stereoselectively the (S)-isomers from racemic mixtures of secondary alcohols leaving their antipodes unaffected in Tris-HCl buffer. Those substrates which afforded the best results in the kinetic resolution were subjected to a chemo-enzymatic sequence of deracemization. G. jasminoides immobilized cells in calcium alginate were used for the oxidation of the (S)-enantiomers and, in a second step, NaBH4 was added to the same vessel for the reduction of the corresponding ketone. The sequential repetition of these two steps allowed obtaining the R-alcohols in 82-90% yield in high optical purity (71-96% ee). Despite the viability of the cells is affected by the chemical reagent, their enzymes remain active due to the protective environment of the calcium alginate beads.