Engineered amine oxidase for efficient oxidative dehydroaromatization of 1,2,3,4-tetrahydroquinolines toward quinolines in aqueous media

Abstract

The oxidative dehydroaromatization (ODA) of 1,2,3,4-tetrahydroquinoline (THQ) is a highly atom economic route for the synthesis of quinoline, a privileged N-heterocyclic motif in the pharmaceutical industry, while requiring stoichiometric strong oxidants and noble metal catalysts. Amine oxidase (AO)-catalyzed oxidative dehydroaromatization of THQs is a sustainable alternative but still suffers from low activity and a narrow substrate scope. Herein, a novel amine oxidase from Vibrio sp. JCM 19236 (VsAO) was obtained by gene mining and its mutant M2(F368D/N127K) was obtained by protein engineering. VsAO exhibited higher ODA activity over the reported AOs due to the unique dual-tunnel structure for substrates/products entrance/exit. M2 exhibited higher enzyme activity owing to the narrowed port and enhanced positivity at the tunnel that is close to the isoalloxazine ring head of flavin adenine dinucleotide (FAD), pushing the substrate closer to the isoalloxazine catalytic center of FAD and leading to higher enzymatic activity and higher catalytic performance.