Highly Selective Indole Oxidation Catalyzed by a Mn-Containing Artificial Mini-Enzyme

Abstract

Indole oxidation represents a real challenge for selectivity because it typically leads to complex mixtures of products even when highly selective enzymes are used. Here, we describe the catalytic potential of an artificial enzyme, Mn-Mimochrome VI*a (Mn-MC6*a), in promoting indole oxidation. This mini-enzyme contains a manganese-deuteroporphyrin active site within a scaffold of two synthetic small peptides covalently linked to porphyrin. Mn-MC6*a promotes the selective oxidation of indole at its C3 position, leading to a 3-oxindole derivative (2-TFE-3-oxindole) with unprecedented product selectivity (86% at pH 8.5) compared to native or artificial heme-enzymes. We also suggest a possible reaction mechanism based on the effect of pH, cosolvent, and indole substitution on the reaction outcome. These studies demonstrate that Mn-MC6*a is an excellent artificial peroxygenase for the production of 3-oxindole-containing compounds as key building blocks for the synthesis of fine chemicals.