Solvent‐Free Regioselective Synthesis of Fluorescent Pyridopyrimidiniums: Application Toward DNA Binding, Antibiofilm, and Antimicrobial Studies

Regioselective solvent‐free synthesis of water‐soluble polycyclic quaternary N ‐bridgehead pyridopyrimidinium ions in good yield (up to 90%) has been demonstrated. Two libraries of pyridopyrimidiniums with different skeletal pattern have been synthesized. A significant fluorescent enhancement has been observed when a particular tetracyclic pyridopyrimidinium probe 3b was treated with calf thymus DNA (CT‐DNA), displaying its strong DNA binding properties. The binding constant value obtained from UV–vis spectral analysis is 2.6 × 10 5 M −1 . Compound 3b also displaced ethidium bromide from ethidium bromide‐DNA complex, thereby proving it as a strong DNA intercalator. 3b shows promising antimicrobial and anti‐biofilm activities against Staphylococcus aureus ( S. aureus ). All the relevant studies established it as a potential bioactive DNA‐binding agent. A detailed comparative study of 3a and its demethyl analogue 3b to demonstrate structure activity–relationship has also been documented.