Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[]quinolizinium derivatives by Palladium-mediated cross-coupling reactions.

9-Arylbenzo[]quinolizinium derivatives were prepared with base-free Suzuki-Miyaura coupling reactions between benzo[]quinolizinium-9-trifluoroborate and selected benzenediazonium salts. In addition, the Sonogashira coupling reaction between 9-iodobenzo[]quinolizinium and the arylalkyne derivatives yielded four novel 9-(arylethynyl)benzo[]quinolizinium derivatives under relatively mild reaction conditions. The 9-(,-dimethylaminophenylethynyl)benzo[]quinolizinium is only very weakly emitting, but the emission intensity increases by a factor >200 upon protonation, so that this derivative may operate as pH-sensitive light-up probe. Photometric and fluorimetric titrations of duplex and quadruplex DNA to 9-(arylethynyl)benzo[]quinolizinium derivatives revealed a significant binding affinity of these compounds towards both DNA forms with binding constants of = 0.2-2.2 × 10 M.