Reactions of the vitamin E model compound 2,2,5,7,8-pentamethylchroman-6-ol with peroxyl radicals.
The vitamin E model compound 2,2,5,7,8-pentamethylchroman-6-ol (1b) was oxidized by peroxyl radicals generated by thermolysis of 2,2'-azobis(2,4- dimethylvaleronitrile) in oxygenated solvents. Oxidation of 1b yielded 4a,5-epoxy-4a,5-dihydro-8a-hydroperoxy- 2,2,5,7,8-pentamethylchroman-6(8aH)-one (5b), 7,8-epoxy-7,8-dihydro-8a-hydroperoxy-2,2,5,7,8-pentamethylchroman- 6(8aH)- one (6b), 8a-[(2,4-dimethyl-1-nitrilopent-2-yl)dioxy]-2,2,5,7,8- pentamethylchroman-6(8aH)-one (3b), and a 5,5'-spirodimer product (7b). In otherwise identical reactions, yields of chromanone 3b and epoxides 5b/6b increased with increasing solvent polarity, whereas the yield of spirodimer 7b decreased. Deuterium substitution at C5a inhibited oxidation of 1b to spirodimer 7b and favored the formation of a novel 5,7'-spirodimer 11. The results demonstrate that the reaction medium controls the balance between competing reactions of chromanoxyl radical 2b and are consistent with the formation of epoxides and 8a-substituted tocopherones as the predominant products of alpha-tocopherol oxidation in biological membranes.
Liebler
D C
DC
Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721.
Burr
J A
JA
Matsumoto
S
S
Matsuo
M
M
D000975:Antioxidants / Q000737:chemistry*; D002839:Chromans / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry*; D012997:Solvents; D013329:Structure-Activity Relationship; D014810:Vitamin E / Q000737:chemistry*
D000975:Antioxidants; D002839:Chromans; D010545:Peroxides; D012997:Solvents; D014810:Vitamin E; C029141:2,2,5,7,8-pentamethyl-1-hydroxychroman