Enantioselective hydrolysis of styrene oxide with the epoxide hydrolase of Sphingomonas sp. HXN-200

The soluble bacterial epoxide hydrolase (EH) from Sphingomonas sp. HXN-200 catalyzed the enantioselective hydrolysis of racemic styrene oxide to give (S)-styrene oxide with an enantiomeric ratio (E) of 21-23 in aqueous buffer, better than any reported native EHs. The ring opening of the styrene oxide with this EH was only at the terminal position for the (S)-enantiomer and at the terminal and benzylic position in an 87:13 ratio for the (R)-enantiomer. Enzymatic hydrolysis of the styrene oxide in a two-liquid phase system significantly reduced autohydrolysis, thus improving the E to 26-29. Hydrolysis of 160 mM styrene oxide with cell-free extract (CFE) of Sphingomonas sp. HXN-200 (10 mg protein/mL) in aqueous buffer and n-hexane (1:1) for 30.7 h afforded 39.2% (62.7 mM) of (S)-styrene oxide in >99.9% ee. The lyophilized CFE was proven to be stable, while the rehydrated lyophilized CFE powder was successfully used for the hydrolysis of 320 mM styrene oxide in the two-liquid phase system, yielding 40.2% (128.6 mM) of (S)-styrene oxide in >99.9% ee after 13.8 h. No inhibitory effect of the diol product on the hydrolysis was observed when the diol concentration was lower than 476 mM, suggesting a straightforward process for the hydrolysis of up to 1 M styrene oxide.