Cholesterol-diaryl ketone stereoisomeric dyads as models for clean type I and type II photooxygenation mechanisms.

Autores de IIS La Fe

• Inmaculada Andreu Ros

  Autor

• Isabel Maria Morera Bertomeu

  Autor

• Laura Sanchez Casado

  Autor

• Miguel Ángel Miranda Alonso

  Autor

Participantes ajenos a IIS La Fe

• Boscá F
• Camps P

Abstract

Cholesterol (Ch) is a major target for oxidative degradation in cell membranes, a process which can occur by two mechanisms: Type I (via free radicals) and Type II (mediated by 1O2). In the present work, several dyads have been synthesized from beta- and alpha-Ch and ketoprofen (KP) or tiaprofenic acid (TPA). Upon irradiation under anaerobic conditions, KP-alpha-Ch dyads were efficiently photolyzed, via intramolecular hydrogen abstraction from C-7. By contrast, KP-beta-Ch, TPA-alpha-Ch, and TPA-beta-Ch remained unchanged after prolonged irradiation. The transient absorption spectra of KP-alpha-Ch were assigned to the short-lived biradicals resulting from intramolecular hydrogen abstraction. Interestingly, the spectra and lifetimes obtained for the TPA-derived dyads were very similar to those of the TPA triplet excited state. For the KP-alpha-Ch dyads, generation of singlet oxygen was expectedly negligible. Conversely, for TPA-alpha-Ch a Phi delta) value as high as 0.5 was determined. Thus, KP-based dyads are appropriate models for clean type I Ch oxidation, whereas the TPA derivatives are suitable systems for investigation of the purely type II process.

Keywords

• SINGLET OXYGEN; HYDROGEN ABSTRACTION; ALLYLIC HYDROGENS; BENZOPHENONE; PHOTOLYSIS; ACID; PHOTOCHEMISTRY; PEROXIDATION; KETOPROFEN; OXIDATION