PREPARATION AND CHARACTERIZATION OF 8A-(PHOSPHATIDYLCHOLINE-DIOXY)-ALPHA-TOCOPHERONES AND THEIR FORMATION DURING THE PEROXIDATION OF PHOSPHATIDYLCHOLINE IN LIPOSOMES

alpha-Tocopherol was reacted with the phosphatidylcholines (PCs), 1-pa lmitoyl-2-linoleoyl-3-sn-PC (PLPC), 1-palmitoyl-2-linolenoyl-3-sn-PC, 1-palmitoyl-2-arachidonoyl-3-sn-PC (PAPC) and 1-stearoyl-2-arachidonoy l-3-sn-PC, in the presence of the free radical initiator, 2,2'-azobis( 2,4-dimethylvaleronitrile), at 37 degrees C. The addition products of alpha-tocopherol with the PC peroxyl radicals were isolated and identi fied as 8a-(PC-dioxy)-alpha-tocopherones, in which the peroxyl radical s derived from each PC molecule attacked the 8a-position of the alpha- tocopheroxyl radical. The antioxidative efficiency of alpha-tocopherol against the peroxidation of PLPC and PAPC in liposomes was assessed b y the formation of the reaction products of alpha-tocopherol. When alp ha-tocopherol was oxidized in the presence of the water-soluble free r adical initiator, 2,2'-azobis(2-amidinopropane) dihydrochloride, epoxy -alpha-tocopherylquinones were mainly produced together with 8a-(PC-di oxy)-alpha-tocopherones and alpha-tocopherylquinone. The yield of alph a-tocopherylquinone was increased by treating each sample with dilute acid which indicates the presence of tocopherone precursors other than the 8a-(PC-dioxy)-alpha-tocopherones. The same products were also det ected from iron-dependent peroxidation, although the yields were very low.