Useful 1O2 (1Δg) generator, 3‐(4′‐methyl‐1′‐naphthyl)‐propionic acid, 1′,4′‐endoperoxide (NEPO), for dioxygenation of squalene (a skin surface lipid) in an organic solvent and bacterial killing in aqueous medium

Abstract

3‐(4′‐Methyl‐1′‐naphthyl)‐propionic acid, 1′,4′‐endoperoxide (NEPO) provides singlet state of oxygen (¹O₂, ¹Δ_g) at 37°C in sodium phosphate buffer (pH 7.2), acetate buffer (pH 4.5), methanol or chloroform, through the retro‐Diels‐Alder reaction. The total amount of ¹O₂ generated by NEPO was calculated using the following equation: [¹O₂]=[NEPO]₀[1−exp^−kt], where [¹O₂], [NEPO]₀ and k are the total amount of ¹O₂ produced during the time t, initial concentration of NEPO and the first‐order reaction rate constant, respectively. When squalene was exposed to ¹O₂ which was generated thermolytically from NEPO, it was oxidized to three hydroperoxides, mono‐, di‐ and tri‐hydroperoxides, in amounts proportional to the dose of NEPO. The oxidizability of squalene was much more extensive compared with unsaturated phospholipids. Additionally, when wild‐type E. coli and lycopene‐producing mutant E. coli were exposed to NEPO‐derived ¹O₂, there was significant loss of viability of wild‐type E. coli but no significant loss of viability in lycopene‐producing strain, suggesting that lycopene by scavenging ¹O₂ protected E. coli against ¹O₂ toxicity.