Synthesis, characterization and photodynamic activity of amino-substituted hypocrellin derivatives

Three new hypocrellin derivatives, amino- or amino acid-substituted on the side ring of hypocrellin B (HB), were synthesized by the reactions of HB with 3-methoxypropylamine, 6-aminohexanoic acid and gamma-amino-n-butyric acid, respectively. The structures of these compounds were characterized with proton nuclear magnetic resonance spectra, infrared spectra and mass spectra. The UV-visible absorption spectra, singlet oxygen-generating quantum yield and amphiphilicities of hypocrellin derivatives were measured and compared with HB, the parent compound. These derivatives showed strong absorption in the domain of the phototherapeutic window (600-900 nm) and improved amphiphilicity. HB and the derivatives were preliminarily tested for their photodynamic effects on human oral cavity epithelial carcinoma KB cell line in vitro. Two amino acid-substituted hypocrellins showed phototoxicity to the KB cell line. At an inhibitory dosage of 50% killing only 0.51 mumol L-1 compound 3 (or 0.88 mumol L-1 compound 2) and 0.5 J cm-2 irradiation were required. The hypocrellins exhibited some dark toxicity to the KB cell line. HB and amino acid-substituted hypocrellins showed lower dark toxicity to the KB cell line than amino-substituted hypocrellins in the assessment of cell survival.