Cationic hypericin derivatives as novel agents with photobactericidal activity: synthesis and photodynamic inactivation of Propionibacterium acnes.

The present communication describes for the first time the synthesis and preliminary testing of two cationic hypericin derivatives. Uncharged hypericin derivatives with omega,omega'-attached C2-linkers leading to a pyridyl or a 4-dimethylaminophenyl residue were prepared and subsequently quaternized by means of iodomethane. Photobactericidal activity was assessed using Propionibacterium acnes. The quaternary N,N,N-trimethyl-anilinium derivative displayed a pronounced photodynamic inactivation of the bacteria at low incubation concentrations (<100 nm) and a short incubation time (1 h) after illumination with yellow light (590 nm, 20 J cm(-2)), whereas the photobactericidal efficacy of the N-methyl-pyridinium derivative was negligible under identical experimental conditions.