Toluene Dioxygenase-Catalysed Oxidation of Benzyl Azide to Benzonitrile: Mechanistic Insights for an Unprecedented Enzymatic Transformation

Abstract

Enzymatic dioxygenation of benzyl azide by toluene dioxygenase (TDO) produces significant amounts of the cis-cyclohexadienediol derived from benzonitrile, along with the expected azido diols. We demonstrate that TDO catalyses the oxidation of benzyl azide to benzonitrile, which is further dioxygenated to produce the observed cis-diol. A proposed mechanism for this transformation involves initial benzylic monooxygenation followed by a nitrene-mediated rearrangement to form an oxime, which is further dehydrated to afford the nitrile. To the best of our knowledge, this is the first report of enzymatic oxidation of an alkyl azide to a nitrile. In addition, the described oxime-dehydration activity has not been reported for Rieske dioxygenases.

Keywords: Rieske; azides; biocatalysis; dioxygenases; oxidation.