Enzymatic oxidation of alkenes

Laccase (EC 1.10.3.2) from the white-rot fungus Trametes hirsuta was used to oxidize alkenes. The oxidation was the effect of a two-step process, in which the enzyme first catalyzed the oxidation of primary substrate, the mediator, and then the oxidized mediator oxidized the secondary substrate, the alkene. Three different mediators were studied in the oxidation of aliphatic and cyclic alkenes.All the alkenes tested were oxidized, but the degree of conversion depended on the alkene and mediator used. The mediators differed from each other in optimal reaction conditions and in specificity towards a given alkene. The best results were obtained by using hydroxybenzotriazole as mediator. Aliphatic polyunsaturated and aromatic allyl alcohols were completely oxidized within 2 h at 20°C. Aliphatic allyl alcohols were oxidized up to 70% at 45°C for 20 h, whereas a conversion of 60% was achieved in 5 h under oxygen atmosphere. By contrast, the oxidation degree of other alkenes, such as allyl ether, cis-2-heptene and cyclohexene, remained low with all the mediators and did not exceed 25%. The major oxidation products in all cases were the corresponding ketones or aldehydes.