Functional Group Diversity in Enzymatic Oxygenation Reactions Catalyzed by Bacterial Flavin-Containing Cyclohexanone Oxygenase

The bacterial flavoprotein monooxygenase cyclohexanone oxygenase was found by spectrophotometric NADPH consumption assays and product analysis studies to perform oxygenation reactions on ketones, aldehydes, sulfides, selenides, boronic acids, a phosphite ester, and an iodide ion. Kinetic parameters (K_m, V_max) are reported for these substrates. The relevance of these results to possible active oxygen-transfer species in this enzyme is discussed. The potential utility of boronic acids as general probes for nucleophilic oxygen-transfer capability in oxygenases and in model chemistry is analyzed. The potential utility of cyclohexanone oxygenase as an enatioselective and/or chemoselective oxidant for organic molecules is assessed. Unsuccessful attempts at exploiting the 2,3-sigmatropic rearrangement of allyl sulfoxides and allyl selenoxides for mechanism-based inactivation of cyclohexanone oxygenase are reported. The use of the facile 2,3-sigmatropic rearrangement of allyl selenoxides to generate electrophilic allyl selenates for the design of mechanism-based inactivators for other enzymes is proposed.