Enzyme-Mimetic Photo-decarboxylation Based on Geometry-Dependent Supramolecular Association

Abstract

Natural enzymes rely on their active center for geometric recognition of their substrates, which contributes to their catalytic properties. Achieving enzyme-like binding in artificial systems remains a challenge, particularly for molecular catalysts and substrates that have distinct shapes. Herein, we report the association of amino acids, tethered with a cleavable tricyclic fluorenyl moiety, to the flavin-based photocatalyst of complementary shapes, with aromatic stacking as the driving force, to perform the photocatalytic decarboxylation of amino acids. Our experimental and theoretical results indicate that the stacking of the fluorenyl moiety to flavin resulted in location of the flavin proximal to the α-carbon of the amino acid. As a result, the efficiency of the decarboxylation reactions, which occurred at the α-carbon of the amino acid, was significantly improved, followed by addition of hydroxyl or oxygen under aerobic conditions. In contrast, considerably lower efficiency in decarboxylation reactions was observed when the amino acids were unmodified or modified with a tert-butyl or benzyl moiety, in which the α-carbon was located away from the catalyst, confirming the importance of the flavin–fluorenyl recognition and the proximity effect to the catalytic activity. Moreover, photo-decarboxylation and oxygenation was observed for a short peptide that has a carboxylate at the α-carbon close to the fluorenyl moiety. Our findings provide a method to create catalyst–substrate recognition and may aid in the future design of bioinspired catalytic systems.