Synthesis of Fluorescent, DNA-Binding Benzo[ b ]indolonaphthyridinium Derivatives by a Misguided Westphal Condensation.

A novel type of azoniahetarene, namely, benzo[ b ]indolonaphthyridinium, was unexpectedly formed by the reaction of N -alkylated β-carbolinium derivatives and the enolizable 1,2-cyclohexadione under typical conditions of a Westphal reaction. The products exhibit high fluorescence intensities in polar solvents (Φ fl = 0.52-0.67) and bind to DNA by intercalation with high affinity ( K b = 1.5 × 10 6 M -1 ). Furthermore, under the same conditions, DNA-binding sempervirine derivatives were synthesized in a Westphal reaction from 1,2-diketones that have at least one non-enolizable α-carbon atom, which shows that the reaction pathway is determined by the substrate structure.