Oxidation of ultrafast radical clock substrate probes by the soluble methane monooxygenase from Methylococcus capsulatus (Bath)

Radical clock substrate probes were used to assess the viability of a discr ete substrate radical species in the mechanism of hydrocarbon oxidation by the soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bat h). New substituted cyclopropane probes were used with very fast ring-openi ng rate constants and other desirable attributes, such as the ability to di scriminate between radical and cationic intermediates. Oxidation of these s ubstrates by a reconstituted sMMO system resulted in no rearranged products , allowing an upper limit of 150 fs to be placed on the lifetime of a putat ive radical species. This limit strongly suggests that there is no such sub strate radical intermediate. The two enantiomers of trans-1-methyl-2-phenyl -cyclopropane were prepared, and the regioselectivity of their oxidation to the corresponding cyclopropylmethanol and cyclopropylphenol products was d etermined The results are consistent with selective orientation of the two enantiomeric substrates in the hydrophobic cavity at the active site of sMM O, specific models for which were examined by molecular modeling.