Exploitation of laccases for the oxidation of new and old subsrates

Laccases are oxidoreductases belonging to the multinuclear copper-containing oxidases. The overall outcome of their catalytic cycle is the reduction of one molecule of oxygen to two molecules of water and the concomitant oxidation of four substrate molecules to give four radicals.1 Typical substrates of laccases are phenols and aliphatic or aromatic amines, the reaction products being mixtures of dimers or oligomers derived by the coupling of the reactive radical intermediates. For instance, this biotransformation has been exploited to isolate new dimeric derivatives of natural phenolic derivatives (resveratrol and its analogues, chalcones, ...).2 As far as aromatic amines concerns, we have recently reported the results obtained in the oxidation of vinyl amines (i.e., 1)3 and we are currently investigating the oxidation of ortho-substituted diamines, i.e. the previously described compound 2.4 In other studies, years ago we described the use of laccase-catalyzed reactions for the selective C-C coupling of highly substituted phenols, like ?-estradiol and totarol.5 Recently updates of this biocatalyzed reactions have been obtained with the enantiomers of trans-8-hydroxycalamenene (3)