Nitric oxide-induced oxidation of alpha-tocopherol.

Exposure of alpha-tocopherol (alpha-T) to nitric oxide under aerobic conditions resulted in a complex oxidation process whose final outcome was dictated by the nature of the reaction medium. In a cyclohexane solution, a prevailing route led to a mixture of relatively unstable polar products positive to Griess reagent. On standing at room temperature these were partially converted to the novel 2,3-dimethyl-4-acetyl-4-hydroxy-5-nitroso-2-cyclopentenone derivative. Reaction of alpha-T via a secondary oxidation path led to the formation of alpha-tocopherylquinone (alpha-TQ) as well as of little amounts of the corresponding nitrite ester. A quite different product pattern was observed when the reaction was carried out on a suspension of alpha-T in 0.1 M phosphate buffer, pH 7.4. Besides a significant formation of alpha-TQ and its nitrite ester, product analysis revealed a characteristic pattern of apolar compounds consisting of a yellow dimer and a series of related oligomers. These results provide an improved chemical background to inquire into the role of alpha-T in nitric oxide-induced tissue injury.