C–N coupling of 3-methylcatechol with primary amines using native and recombinant laccases from Trametes versicolor and Pycnoporus cinnabarinus

Five laccase genes from Pycnoporus cinnabarinus and Trametes versicolor encoding for different isoenzymes have been cloned, recombinantly expressed and characterized. Following C–N coupling of primary linear, branched-chained and cyclic amines to 3-methylcatechol was mediated by native and recombinant laccases yielding the corresponding secondary amines. Formation of C5-monoaminated ortho-methylquinones occurred within 1–2 h; prolonged incubation led to the formation of high-molecular mass products. No difference between the use of native or recombinant isoenzymes from P. cinnabarinus or T. versicolor was observed. Optimization of the reaction conditions included variation of amine donor ratios, pH, amount and type of enzyme preparations. The formation of by-products could be suppressed at pH values corresponding to the enzymes optima (pH 4–5). A total of 10 secondary amines were synthesized with product formations of up to 80%. Furthermore, all purified secondary amines were characterized by NMR-, LC–MS- and HRMS-analysis and log P values were determined.