Mechanistic Investigation of Oxidative Decarboxylation Catalyzed by Two Iron(II)- and 2-Oxoglutarate-Dependent Enzymes.

Two non-heme iron enzymes, IsnB and AmbI3, catalyze a novel decarboxylation-assisted olefination to produce indole vinyl isonitrile, an important building block for many natural products. Compared to other reactions catalyzed by this enzyme family, decarboxylation-assisted olefination represents an attractive biosynthetic route and a mechanistically unexplored pathway in constructing a C═C bond. Using mechanistic probes, transient state kinetics, reactive intermediate trapping, spectroscopic characterizations, and product analysis, we propose that both IsnB and AmbI3 initiate stereoselective olefination via a benzylic C-H bond activation by an Fe(IV)-oxo intermediate, and the reaction likely proceeds through a radical- or carbocation-induced decarboxylation to complete C═C bond installation.

In Vitro Stepwise Reconstitution of Amino Acid Derived Vinyl Isocyanide Biosynthesis: Detection of an Elusive Intermediate.

In vitro reconstitution of a newly discovered isonitrile synthase (AmbI1 and AmbI2) and the detection of an elusive intermediate (S)-3-(1H-indol-3-yl)-2-isocyanopropanoic acid 1 in indolyl vinyl isocyanide biogenesis are reported. The characterization of iron/2-oxoglutarate (Fe/2OG) dependent desaturases IsnB and AmbI3 sheds light on the possible mechanism underlying stereoselective alkene installation to complete the biosynthesis of (E)- and (Z)-3-(2-isocyanovinyl)-1H-indole 2 and 5. Establishment of a tractable isonitrile synthase system (AmbI1 and AmbI2) paves the way to elucidate the enigmatic enzyme mechanism for isocyanide formation.