Boron-dipyrromethene derivatives bearing N-alkyl phthalimide and amine substituents of potential application in the photoinactivation of bacteria

Abstract

Novel boron-dipyrromethene derivatives with N-alkyl phthalimide and amine substituents, including iodinated derivative, were synthesized and characterized using UV–Vis spectrophotometry, mass spectrometry (HRMS) and NMR spectroscopy. Non-iodinated analogs revealed high emission properties with fluorescence quantum yields (ΦF) between 0.48 and 0.58. But singlet oxygen generation quantum yields (ΦΔ) were low with values in the range of 0.01–0.06. Iodinated derivative revealed a strong heavy atom effect resulted in the red-shifted absorption and emission bands, fluorescence quenching with ΦF values of about 0.02, but increased singlet oxygen generation abilities with excellent ΦΔ values of 0.97 and 0.85 in methanol and ethanol, respectively. In vitro photodynamic inactivation activity was evaluated on Gram-positive cocci of Staphylococcus aureus and Gram-negative rods of Escherichia coli. Novel BODIPY derivatives showed promising inactivation efficiency on S. aureus, with the highest activity for iodinated derivative, which reduced the number of bacteria by 3.6 logs10 at low 0.5 μM concentration. However, none of the tested derivatives showed a satisfactory ability to eradicate E. coli. Only non-iodinated derivative with amine substituent, at high concentrations, showed some significant activity with log10 reduction values of 2.0 and 1.1 at 500 and 50 μM, respectively. Nevertheless, the presented approach enabled to obtain novel BODIPY derivatives with promising photoinactivation activity and properties such as fluorescence and singlet oxygen generation efficacy, easy to modify by the heavy atom substitution. Also, peripheral phthalimide or amine groups can be used for further structural modifications.