Catalytic turnover of benzylamine by a model for the lysine tyrosylquinone (LTQ) cofactor of lysyl oxidase

Lysyl oxidase differs from other copper amine oxidases in that its active quinone cofactor reflects cross-linking of a lysyl residue into the tyrosine-derived quinone nucleus found in the plasma and other copper amine oxidases. A model for the lysyl oxidase cofactor (LTQ), 3,3-dimethyl-2,3-dihydroindole-5,6-quinone (4), was synthesized and found to be stable to both hydrolysis and oxidation events that prevent simpler models from functioning as turnover catalysts. We show that 4 catalyzes the aerobic oxidative deamination of benzylamine, though turnover eventually ceases on account of oxidation of the dihydrobenzoxazole tautomer of the "product Schiff base" to form a benzoxazole, a reaction that may be physiologically relevant. The mechanism of the overall reaction profile was elucidated by a combination of optical and NMR spectroscopy and O(2) uptake studies.