title: Novel oxidations of (+)-catechin by horseradish peroxidase and laccase.
abstract: Horseradish peroxidase (HRP; EC 1.11.1.7) catalyzed the H(2)O(2)-dependent oxidative coupling of (+)-catechin 1 to form three different biphenyl C-C dimers 2-4, whereas Rhus vernicifera laccase catalyzed the formation of two new catechin-hydroquinone adducts 5 and 6. Spectroscopic evidence showed that HRP dimers were linked through position 8 of the A-ring of one catechin moiety to C-5' of ring B in 2 and 4 and to C-2 of ring C in 3. The unusual catechin dicarboxylic acid dimer 4 was obtained by ortho cleavage of the E-ring. Hydroquinone served as both a shuttle oxidant and a reactant by coupling at C-2' and C-5' of the catechin B-ring during laccase oxidations. HRP and laccase oxidation products were compared to D,L-alpha-tocopherol and (+)-catechin for their abilities to inhibit iron-induced lipid peroxidation in rat brain homogenates and Fe(3+)-ADP/NADPH in rat liver microsomes, as measured by the intensity of thiobarbituric acid reactive substance. All metabolites exhibited anti-lipid peroxidation with IC(50) values approximately 2-8 times higher than those of standard compounds. Characteristic reaction products may prove to be novel markers for (+)-catechin antioxidant reactions in living systems.
authors.affiliation: Medicinal and Natural Products Chemistry and Center of Biocatalysis and Bioprocessing, College of Pharmacy, The University of Iowa, Iowa City 52242, USA.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Hosny
authors.forename: John P N
authors.initials: JP
authors.lastname: Rosazza
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002392:Catechin / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D019281:Dimerization; D006735:Horseradish Peroxidase / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006873:Hydroquinones / Q000737:chemistry / Q000378:metabolism; D007501:Iron / Q000494:pharmacology; D042845:Laccase; D015227:Lipid Peroxidation / Q000187:drug effects; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D016339:Spectrometry, Mass, Fast Atom Bombardment; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D024502:alpha-Tocopherol / Q000494:pharmacology
chemical_list: D006873:Hydroquinones; D017392:Thiobarbituric Acid Reactive Substances; D002392:Catechin; D006861:Hydrogen Peroxide; D007501:Iron; D010088:Oxidoreductases; D042845:Laccase; D006735:Horseradish Peroxidase; D024502:alpha-Tocopherol; C031927:hydroquinone