Biooxidation of ketones with a cyclobutanone structural motif by recombinant whole-cells expressing 4-hydroxyacetophenone monooxygenase

Whole cells of an Escherichia coli strain overexpressing 4-hydroxyacetophenone monooxygenase (HAPMO) originating from Pseudomonas fluorescens ACB have been used to study the stereopreference in the Baeyer–Villiger reaction of ketones bearing a cyclobutanone structural motif. The enzyme catalyzes the oxidation of several prochiral cyclobutanones to antipodal butyrolactones as obtained in cyclohexanone monooxygenase mediated conversions. However, chemical yields and enantiomeric purity are usually moderate. The regioselectivity in oxidations of fused cylobutanones differs from the previously observed behavior for Baeyer–Villiger monooxygenases with highly varying ratios of “normal” and “abnormal” product lactones and enantioselectivities. Taken together with previous substrate profiling data, HAPMO represents a distinctively different biocatalytic entity compared to monooxygenases characterized so far.