Nature has evolved a variety of remarkably efficient metalloenzymes for the selective oxygenation of even the most unreactive C–H bonds. Copper-containing particulate methane monooxygenases (pMMO), and the  non-heme diiron enzymes sMMO and AlkB allow microorganisms to grow on natural gas and petroleum as their sole sources of carbon. Cytochrome P450s and fungal APOs are heme-thiolate enzymes that generate an oxoiron(IV)-porphyrin π-radical cation (compound I) as the highly reactive intermediate to functionalize substrates. Non-heme iron proteins such as TauD and SyrB2 break strong C–H bonds using a ferryl species, Fe(IV)=O. By distinct contrast, lipoxygenases employ hydroxoiron(III) or manganese(III) as reactive intermediates to activate allylic C–H bonds. APO compound II [Cys-Fe(IV)-OH] is also reactive toward C–H bonds. In this lecture I will discuss recent developments from our lab in the areas of biomimetic metalloporphyrin catalysts and those of novel, heme-thiolate APO biocatalysts with active sites similar to that of cytochrome P450.  Particular emphasis will be on C–H bond cleavage events that have little or no driving force, focusing attention instead on electronic and structural features that affect intrinsic reaction barriers.<br/><br/>

Oxygen activation and C-H bond cleavage by metalloenzymes and metalloporphyrins

253rd National Meeting (2017)

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