The 5H-pyrido[4,3-b]indole, 11H-indolo[3,2-c]quinoline, 5H-benzo[f]pyrido[4,3-b]indole, and 13H-benz[5,6]indolo[3,2-c]quinoline heteroaromatic nuclei have been synthesized by the Graebe−Ullmann method by classical heating or under microwave irradiation. These tri-, tetra-, and pentacyclic compounds were transformed into the corresponding cationic derivatives by N-alkylation, and the DNA-binding properties of the resulting cationic systems were examined using UV−vis spectroscopy, viscometric determinations, and molecular modeling techniques. The tetracyclic cations were transformed into bis-salts by means of a diethyl bispiperidine rigid chain and a more flexible polyamide linker, but the low solubility of these bis-salts made the study of their bisintercalating properties difficult.

The synthesis of new pyrido[1,2-a]- and pyridazino[1,6-a]benzimidazolium salts by basic condensation of 1,3-disubstituted 2-alkylbenzimidazolium salts and 1,2-diketones and subsequent chemical transformations is described. The DNA-binding properties were examined by UV-vis spectroscopy, viscosimetric determinations, and molecular modeling techniques. The presence of a flat polycyclic hydrocarbon moiety such as a naphthalene-1,8-diyl or a biphenyl-o,o'-diyl, fused to the cationic heterocycle, appears to enhance the interaction with DNA. Variation of the substituents on the indole-like N will allow us to build up a new series of bis-salts with bis-intercalating properties.

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A new synthesis of the pyrrolo[1,2-a]pyrazine system from pyrrole is described. In light of the ab initio calculations carried out on this heterocyclic system some of its basic chemistry was investigated and included electrophilic substitution, addition of organolithium reagents, metalation with lithium diisopropylamide and subsequent reaction with electrophiles, and formation of salts by quaternization of the nonbridgehead nitrogen. N-ylides obtained from these salts undergo 1,3-dipolar cycloaddition with suitable dipolarophiles to give dipyrrolo[1,2-a]pyrazines, pyrazolo[1,5-a]-pyrrolo[2,1-c]pyrazines, and heterobetaines. Examples of intramolecular 1,3-dipolar cycloadditions are also reported.

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A new class of DNA intercalators based on the 8H-pyridazino[1‘,6‘:1,2]pyrido[4,3-b]indol-5-inium system in which the cationic nature of the chromophore is provided by a brigdehead quaternary nitrogen has been obtained. These cations along with 10H-indolo[3,2-c]pyridazino[1,6-a]quinolin-5-inium, 13H-dibenz[f,h]indolo[3‘,2‘:3,4]pyrido[1,2-b]cinnolin-10-inium, and 5H-acenaphtho[1‘,2‘:3‘,4‘]pyridazino[1‘,6‘:1,2]pyrido[4,3-b]indol-8-inium were synthesized by the Westphal reaction of carbolinium derivatives with various 1,2-dicarbonyl compounds. When these tetra-, penta-, and heptacyclic heteroaromatic nuclei were evaluated as DNA intercalators using UV−vis spectroscopy, viscometric determinations, and unwinding angle determinations, we found that only the 8H-pyridazino[1‘,6‘:1,2]pyrido[4,3-b]indol-5-inium cations behaved as DNA intercalators. Molecular modeling studies allowed the preferred orientation of the intercalating chromophore within a CpG intercalation site to be explored and will provide help in the rational design of novel bis-intercalators based on these chromophores.

A simple and efficient method for the cleavage of tertbutoxycarbonyl amides and amines is described, which takes place on silica gel under microwave irradiation.