Structural analysis of hydroperoxides formed by oxidation of phosphatidylcholine with singlet oxygen

Soybean phosphatidylcholine (PC) and dilinoleoyl PC (di-18∶2 PC) were oxidized with singlet molecular oxygen using methylene blue as the photosensitizer. The oxidation products, PC monohydroperoxides (PC-MHP) and PC dihydroperoxides (PC-DHP), were isolated by reverse phase liquid chromatography, and their structures were analyzed by nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS). Signals for the hydroperoxy proton appeared downfield in NMR spectra of PC-MHP and PC-DHP. Soybean PC-MHP and di-18∶2 PC-MHP were converted to trimethylsilyl (TMS) derivatives of hydrogenated diglycerides when treated with phospholipase C and hydrogenated. Thetert-butyldimethylsilyl (TBDMS) derivatives of hydrogenated diglycerides were also prepared from di-18∶2 PC-MHP. Fragmentation of the TMS and TBDMS derivatives was obtained in electron impact mass spectra. The isomeric composition of hydroperoxylinoleate component in di-18∶2 PC-MHP was determined by methanolysis of the hydrogenated diglyceride and mass chromatographic analysis of the resulting isomeric hydroxy octadecanoates.