Asymmetric hydrolysis of racemic para-nitrostyrene oxide using an epoxide hydrolase preparation from Aspergillus niger

A lyophilized epoxide hydrolase preparation was isolated from the fungus Aspergillus niger. The preparation could be used in place of the whole mycelium as biocatalyst for the enantioselective hydrolysis of racemic para-nitrostyrene oxide. The cosolvent used for substrate dissolution showed slightly different effects on enzyme activity and stability. Dimethylsulfoxide (DMSO) was selected as the less inhibitory cosolvent among those tested. The enzyme preparation was first proved efficient by running a batch reactor at a low substrate concentration of 4 mM. The hydrolysis of para-nitrostyrene oxide was fast (around 5 h) and with high enantioselectivity (E = 41). The (S) enantiomer of the epoxide remained in the reaction mixture with an enantiomeric excess (ee) higher than 97% for a conversion of 47%. The substrate concentration had been optimized. It could be increased to 330 m,M (54 g l^-1 without affecting the ee; therefore, the method is potentially useful for the preparative resolution of epoxides. Applications are in the field of chiral synthons which are important building blocks in organic synthesis.