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.