Synthesis and investigation of the DNA-binding and DNA-photodamaging properties of indolo[2,3-b] quinolizinium bromide

The readily available cationic dye 3-Br binds to DNA as was shown by UV, fluorescence and CD spectroscopy. The electronic spectra of the quinolizinium salt 3 exhibit significant bathochromic shifts and a decrease of the absorbance and emission intensity on addition of calf thymus DNA. Moreover, fluorometric titration of [poly(dCdG)]2 with salt 3 resulted in a significant decrease of the emission intensity, whereas addition of [poly(dAdT)]2 led only to a marginal perturbation of the emission spectrum. Analysis of the binding constants with the different polynucleotides revealed that quinolizinium 3-Br binds preferentially to GC base pairs. Irradiation of DNA in the presence of quinolizinium 3-Br resulted in efficient single-strand cleavage of the nucleic acid.