Laccase-mediated multi-step homo- and heteromolecular reactions of ortho-dihydroxylated aromatic compounds and mono- or diaminated substances resulting in C-C, C-O and C-N bonds

Three types of reactions involving oxidation, inter- and intramolecular Michael-addition as well as homo-intermolecular dimerization, catalyzed by laccase [EC. 1.10.3.2] of Pycnoporus cinnabarinus in the presence of oxygen, resulted in the formation of dimeric, trimeric and cyclic products with yields up to 44% (non-optimized reactions). For heteromolecular reactions a number of different aminated five- and six-membered aromatic compounds were used. The first reaction type involved the oxidation of catechol, 3- or 4-methylcatechol to o-quinone and subsequent Michael-addition of the amino compounds with C-N bond formation. Conclusive analytical data (UV-vis data, MS spectra) for the respective o-quinone are provided. The second type of reaction included a homo-intermolecular dimerization probably with C-C and C-O bond formation to the proposed dibenzofuran derivatives. The heteromolecular reaction with the amino compounds yielded trimers consisting of homomolecular dimers and the amino compound connected via a C-N bond. The third reaction type started from epinephrine (adrenaline) which was oxidized by laccase and underwent an intramolecular Michael-addition to adrenochrome. The subsequent heteromolecular reaction resulted in the unusual substance class of cyclooctenes (diazocines). Differences between the reaction types in regard to the kind of o-hydroquinone, amino compound used and the types of product recovered are discussed. (C) 2015 Elsevier B.V. All rights reserved.