Zwitterionic biphenyl quinone methides in photodehydration reactions of 3-hydroxybiphenyl derivatives: laser flash photolysis and antiproliferation study

In aqueous media, photochemical excitation to S(1) of 3-phenylphenols 4-8 leads to deprotonation of the phenol OH, coupled with protonation of the benzyl alcohol and overall dehydration that delivers zwitterions 17-21. The zwitterions react with nucleophiles (CH(3)OH, CF(3)CH(2)OH and ethanolamine) converting them in high quantum yields to the corresponding adducts and photosolvolysis products (for photomethanolysis Φ~0.1-0.5). Zwitterions 20 and 21 were characterized by laser flash photolysis in CH(3)CN-H(2)O (τ~7.5 and 25 μs, respectively) and the associated quenching rate constants with nucleophiles azide and ethanolamine determined. In vitro studies of antiproliferative activity of the photochemicaly generated QMs and zwitterions formed from 2-, 3- and 4-phenylphenols were carried out on three human cancer cell lines HCT 116 (colon), MCF-7 (breast), and H 460 (lung). Irradiation of cells incubated with 3, 6, and 26 showed enhanced antiproliferative activity compared to the cells that were not irradiated.