Reaction of gamma-tocopherol with hypochlorous acid.

In addition to being a very good antioxidant, gamma-tocopherol is also an excellent electrophile trap. This is a study of the reactivity of gamma-tocopherol with hypochlorous acid/hypochlorite, a potential biological foe that is both an oxidant and an electrophile. Aqueous sodium hypochlorite (1.72 mmol; pH 7.4) was stirred with gamma-tocopherol (0.12 mmol) in hexane for 2 min at room temperature. The following products were isolated: gamma-tocopheryl quinone (0.6%), tocored (10%), 3-chloro-gamma-tocopheryl quinone (14%), an ether dimer of 3-chloro-gamma-tocopheryl quinone (0.4%), two isomers of 5-(5-gamma-tocopheryl)-gamma-tocopherol (3 and 2% respectively), 5-chloro-gamma-tocopherol (14%) and two chlorinated dimers (14 and 24% respectively) which were identified as diastereomers of (3R,10R)-11a-chloro-2,3,9,10-tetrahydro-3,5,6,10,12,13-hexamethyl-3,10-bis[(4R,8R)-4,8,12-trimethyltridecyl]-1H-pyrano(3,2a)-8H-pyrano(3,2g)-dibenzofuran-14(7aH)(14aH)-one. The chlorinated dimers, 5-chloro-gamma-tocopherol, 3-chloro-gamma-tocopheryl quinone and its ether dimer are new compounds.

Probucol protects against hypochlorite-induced endothelial dysfunction: identification of a novel pathway of probucol oxidation to a biologically active intermediate.

Atherosclerosis is associated with endothelial dysfunction and a heightened state of inflammation characterized, in part, by an increase in vascular myeloperoxidase and proteins modified by its principal oxidant, hypochlorous acid (HOCl). Here we examined whether probucol could protect against endothelial dysfunction induced by the two-electron oxidant HOCl. Hypochlorous acid eliminated endothelium-dependent relaxation of rabbit aorta, whereas endothelial function and tissue cGMP was preserved and elevated, respectively, in animals pretreated with probucol. Exogenously added probucol also protected against HOCl-induced endothelial dysfunction. In vitro, HOCl oxidized probucol in a two-phase process with rate constants k(1) = 2.7 +/- 0.3 x 10(2) and k(2) = 0.7 +/- 0.2 x 10(2) m(-1) s(-1) that resulted in a dose- and time-dependent accumulation of probucol-derived disulfoxide, 4,4'-dithiobis(2,6-di-tert-butyl-phenol) (DTBP), DTBP-derived thiosulfonate, disulfone, and sulfonic acid, together with 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone (DPQ) as determined by high performance liquid chromatography and mass spectrometry. Like HOCl, selected one-electron oxidants converted probucol into DTBP and DPQ. Also, dietary and in vitro added DTBP protected aortic rings from HOCl-induced endothelial dysfunction and in vitro oxidation by HOCl gave rise to the thiosulfonate, disulfone, and sulfonic acid intermediates and DPQ. However, the product profiles of the in vitro oxidation systems were different from those in aortas of rabbits receiving dietary probucol or DTBP +/- HOCl treatment. Together, the results show that both probucol and DTBP react with HOCl and protect against HOCl-induced endothelial dysfunction, although direct scavenging of HOCl is unlikely to be responsible for the vascular protection by the two compounds.

Characterization of the oxidation products of BO-653 formed during peroxyl radical-mediated oxidation of human plasma.

4,6-Di-tert-butyl-2,3-dihydro-2,2-dipentyl-5-benzofuranol (BO-653) is a novel antioxidant synthesized by theoretical findings and considerations. Here we report on the aqueous peroxyl radical-induced oxidation of human plasma in the presence of BO-653. When BO-653 was given to healthy human subjects at 400 mg twice daily for 28 days, lipids in the resulting plasma were protected from oxidation compared with lipids present in plasma from subjects receiving placebo. Similarly, BO-653 added in vitro at 50 muM inhibited the peroxyl radical-induced accumulation of cholesteryl ester hydroperoxides that occurred in the presence of alpha-tocopherol, although BO-653 did not decrease the rate of consumption of ascorbate, albumin-bound bilirubin, and uric acid. The antioxidant action of in vivo and in vitro added BO-653 was associated with the formation of two major reaction products of BO-653, the structures of which were elucidated by mass spectrometry and nuclear magnetic resonance analyses. The products were identified as stereoisomers of dioxybis(4,6-di-tert.-butyl-2,3,5,7a-tetrahydro-2,2-dipentylbenzofuran-5-one). These dialkylperoxides of BO-653 might be useful markers to assess the antioxidant function of BO-653 in biological systems in vivo.

Reduction of 8a-hydroxy-2,2,5,7,8-pentamethyl-6-chromanone.

Two-electron oxidation of 2,2,5,7,8-pentamethyl-6-chromanol (PH), a model compound of alpha-tocopherol, gives the unstable 8a-hydroxy-2,2,5,7,8-pentamethyl-6-chromanone (POH) which rearranges to form stable 2-(3-hydroxy-3-methylbutyl)-3,5,6-trimethyl-1,4-benzoquinone (PQ). POH and PQ are isomers which have the same oxidation state. The aim of this work was to compare the ease of reduction of POH and PQ at room temperature using a variety of biological and chemical reductants in a reductant:POH (PQ) ratio of 20:1 (or 16:1). Ascorbic acid completely reduced POH to PH in 20 min, but had no effect on PQ after 40 min. Sodium ascorbate did not reduce POH or PQ at all after 40 min. Sodium dithionite reduced POH to PH (85%) in 20 min, but reduced PQ to its hydroquinone, PQH2 (67%) in 40 min. Dithiothreitol produced a slight reduction of POH to PH (21%) but reduced PQ to PQH2 (69%). NADH/FAD reduced POH and PQ to PQH2 (73% and 42%, respectively) in 10 min. It was concluded that POH is easier to reduce than PQ and more likely to form PH as a product, particularly under conditions of mild acidity.