CHAIN-BREAKING NAPHTHOLIC ANTIOXIDANTS - ANTIOXIDANT ACTIVITIES OF POLYALKYLBENZOCHROMANOL, POLYALKYLBENZOCHROMENOL, AND 2,3-DIHYDRO-5-HYDROXY-2,2,4-TRIMETHYLNAPHTHO[1,2-B]FURAN COMPARED TO AN ALPHA-TOCOPHEROL MODEL IN SODIUM DODECYL-SULFATE MICELLES

The antioxidant activities, k(inh), and stoichiometric factors, n, for 6-hydroxy-2,5-dimethyl-2-phytylbenzo[7,8]chroman (2), 6-hydroxy-2,5-dimethyl-2-phytylbenzo[7,8]-3-chromene (3), and 2,3-dihydro-5-hydroxy-2,2,4-trimethylnaphtho[1,2-b]furan (4) were measured in 0.50 M sodium dodecyl sulfate micelles (SDS) by the oxygen uptake method during thermally-initiated peroxidation of polyunsaturated fatty acids (PUFA): linoleic (LA), linolenic (LE), and arachidonic (AR) acids. The k(inh) values of 2-4 were all higher than that of the alpha-tocopherol model compound 6-hydroxy-2,2,5,7,8-pentamethylchroman (1) under all conditions used. For example, the k(inh) of 2 and 4 was 6.60 x 10(4) and 12.6 x 10(4) M(-1) s(-1), respectively, compared to 5.37 x 10(4) for 1 during inhibited peroxidation of LA, initiated by the water-soluble initiator, azobis(amidinopropane-hydrochloride) (ABAP). The antioxidant activities, measured by the k(inh)/k(p) ratios, for 2 (1147), 3 (806), and 4 (1712) were significantly higher than that of 1 (623). Similarly, the k(inh)/k(p) ratios of 2 (792), 3 (601), and 4 (1281) during inhibited peroxidation of LE initiated by lipid-soluble di-tert-butyl hyponitrite (DBHN) were higher than that found for 1 (538), and the k(inh)/k(p) values of 2 (761), 3 (641), and 4 (1006), for inhibited peroxidation of AR initiated by DBHN, were higher than that of 1 (311). The higher antioxidant activities of 2-4 are attributed to enhanced electron delocalization and resulting increased stabilization of the phenolic radicals, compared to that from 1, formed in the rate-determining step of the hydrogen atom transfer reaction to trap peroxyl radicals. The stoichiometric values for peroxyl radical trapping were found for 2 (1.5-1.7), 3 (1.4-1.5), and 4 (1.3-1.5) compared to n = 2 for the model compound 1.