Regioselectivity of Rhodococcus NCIMB 11216 epoxide hydrolase: Applicability of E-values for description of enantioselectivity depends on substrate structure

The regioselectivity of purified epoxide hydrolase from Rhodococcus NCIMB 11216 was investigated by hydrolyzing a series of structurally different epoxides 1a-5a in O-18-labelled water followed by GC/MS analysis of the 1,2-diols formed 1b-5b. The enzyme introduced a single O-18-atom in a trans-specific fashion with a varying degree of regioselectivity depending on the substitution pattern of the substrate. With an aliphatic mono- 1a and 2,2-disubstituted oxirane 3a the attack occurred exclusively at the less hindered C-atom and complete retention of configuration was retained. On the other hand, the regioselectivity was low with a 2,3-di- 4a and a trisubstituted epoxide 5a, and with a substrate bearing a benzylic oxirane atom 2a. As a consequence, the 'Enantiomeric Ratio' (E) can be applied to describe the selectivity of kinetic resolutions for some, but not for all types of substrates. Copyright (C) 1996 Elsevier Science Ltd