Stereoselectivity in the Epoxide Hydrase Catalyzed Hydrolysis of the Stereoisomeric 4-tert-Butyl-1,2-epoxycyclohexanes

Article abstract of DOI:10.1021/jo01290a019

The steric course of the rabbit liver microsome promoted hydrolysis of the racemic cis and trans forms of the title epoxide was investigated. The (+) and (-) forms of c-4-tert-butylcyclohexane-r-1,t-2-diol were the only hydrolysis products, indicating that the enzyme reaction takes place exclusively by diaxial opening of the oxirane ring.The absolute configuration and maximum rotation of this diol were determined by correlation with (1S,3R)-cis-3-tert-butylcyclohexanol.Of the four stereoisomers of the epoxide, the (1S,2R,4S) form was by far the best substrate and the (1R,2S,4S) form the worst.At low conversion, high enantiomeric excesses of the (-)-diol and the (+)-diol were obtained, respectively, from the (+/-)-trans and the (+/-)-cis epoxide; optical purities decreased with increasing conversion.The results are discussed in terms of the helicity of the cyclohexane ring and of the orientation of the tert-butyl group with respect to the oxirane ring.