Fermented solids that contain lipases produced by Rhizopus microsporus have an S-enantiopreference in the resolution of secondary alcohols

Abstract

Lipases are widely used as biocatalysts in the resolution of racemates, where high chemo-, regio- and enantioselectivity are required. In this work, we produced lipases by culturing Rhizopus microsporus in solid-state fermentation. After the fermentation, the solids were dried, producing “Rhizopus microsporus fermented solids” (RMFS). The lipases in RMFS had high activity in the synthesis of ethyl oleate in n-heptane, retaining 100 % activity after 23 successive esterification cycles, each for 4 h at 40 °C. In the kinetic resolution of three aromatic secondary alcohols by transesterification with isopropenyl acetate, in n-heptane, RMFS showed preference for the (S)-enantiomers, in other words, an anti-Kazlauskas enantiopreference. The best results were a conversion of 23 % and an enantiomeric ratio (ESR, i.e. S relative to R) of 26 for resolution of (RS)-1-phenyl-1-ethanol, after 96 h at 40 °C. Since it is rare for lipases to have an (S)-enantiopreference, RMFS have the potential as low-cost biocatalysts for the resolution of racemates of secondary alcohols.