Photodynamic properties of dipeptide-modified hypocrellin B derivatives: the role of tyrosine and tryptophan groups.

Three long-wavelength absorbing dipeptide-modified hypocrellin B (HB) derivatives, Gly-HB, Tyr-HB, and Trp-HB, were prepared for application in photodynamic therapy (PDT). Their abilities to produce free radicals and singlet oxygen were compared in detail with EPR technique, and their binding interactions with calf thymus DNA (CT DNA) were studied by absorption spectra and DNA melting temperature measurements. Tyr-HB and Trp-HB distinguish themselves from Gly-HB and HB remarkably by their significantly improved efficiencies to generate semiquinone anion radicals, superoxide anion radicals, and hydroxyl radicals, as well as their affinity to CT DNA, as the result of the electron-donating properties and intercalating abilities of tyrosine and tryptophan groups. Tyr-HB and Trp-HB show remarkably enhanced photodamage capabilities on CT DNA than their parent HB in aerobic conditions. Moreover, they possess moderate photodamage abilities on CT DNA even in anaerobic conditions, indicating the role of Type I mech...