Enzymatic oxidation of alkenes

Laccase (EC 1.10.3.2) from the white-rot fungus Trametes hirsuta was used t o oxidize alkenes. The oxidation was the effect of a two-step process, in w hich the enzyme first catalyzed the oxidation of primary substrate, the med iator, and then the oxidized mediator oxidized the secondary substrate, the all;ene. Three different mediators were studied in the oxidation of alipha tic 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. Alip hatic polyunsaturated and aromatic allyl alcohols were completely oxidized within 2 h at 20 degrees C. Aliphatic allyl alcohols were oxidized up to 70 % at 45 degrees C for 20 h, whereas a conversion of 60% was achieved in 5 h under oxygen atmosphere. By contrast, the oxidation degree of other alkene s, such as allyl ether, cis-2-heptene and cyclohexene, remained low with al l the mediators and did not exceed 25%. The major oxidation products in all cases were the corresponding ketones or aldehydes. (C) 2000 Elsevier Scien ce B.V. All rights reserved.