Laccase‐Catalysed Homocoupling of Primary Aromatic Amines towards the Biosynthesis of Dyes

Abstract

AbstractColoured disubstituted benzoquinonimine trimeric structures are obtained as main reaction products of the oxidation of p‐electron donor primary aromatic amines using two different laccases, CotA‐laccase from Baccilus subtilus and TvL from Trametes versicolor. These orange‐red to purple products, presenting high molar extinction coefficients, presumably result from oxidative homocoupling reactions, through the formation of NC bonds at positions 2 and 5, of the laccase oxidised intermediate as showed in the proposed oxidative pathway. The product of 1,4‐phenylenediamine is shown to be the trimer known as Bandrowski’s base which has an established role in hair and fur dyeing. Our results also show that the occurrence and/or rates of oxidation of aromatic amines are strongly dependent on the presence of p‐electron releasing substituents in the aromatic ring and are independent on the properties of the enzyme used. Overall our data contribute for (i) understanding key features of laccase reactivity with p‐substituted aromatic amines and (ii) establishing enzymatic processes that lead to the synthesis of coloured bio‐products under mild conditions with potential impact in the cosmetic and dye industries.magnified image