Controlled oxidation of aliphatic CH bonds in metallo-monooxygenases: Mechanistic insights derived from studies on deuterated and fluorinated hydrocarbons

摘要

The control over the regio- and/or stereo-selective aliphatic C-H oxidation by metalloenzymes is of great interest to scientists. Typically, these enzymes invoke host-guest chemistry to sequester the substrates within the protein pockets, exploiting sizes, shapes and specific interactions such as hydrogen-bonding, electrostatic forces and/or van der Waals interactions to control the substrate specificity, regio-specificity and stereo-selectivity. Over the years, we have developed a series of deuterated and fluorinated variants of these hydrocarbon substrates as probes to gain insights into the controlled C-H oxidations of hydrocarbons facilitated by these enzymes. In this review, we illustrate the application of these designed probes in the study of three monooxygenases: (i) the particulate methane monooxygenase (pMMO) from Methylococcus capsulatus (Bath), which oxidizes straight-chain C_1-C_5 alkanes and alkenes to form their corresponding 2-alcohols and epoxides, respectively; (ii) the recombinant alkane hydroxylase (AlkB) from Pseudomonas putida GPo1, which oxidizes the primary C-H bonds of C_5-C_(12) linear alkanes; and (iii) the recombinant cytochrome P450 from Bacillus megaterium, which oxidizes C_(12)-C_(20) fatty acids at the ω-1, ω-2 or ω-3 -CH positions.