New tetracyclic heteroaromatic compounds based on dehydroamino acids: photophysical and electrochemical studies of interaction with DNA

A benzothienoindole (BTIN) and a benzofuroindole (BFIN) were synthesized in high yields, as potential new DNA target compounds, using a metal-assisted intramolecular C-N cyclization of the methyl esters of N-(tert-butoxycarbonyl)-β,β-bis(dibenzothien-4-yl or dibenzofur-4-yl)dehydroalanines. The latter were obtained by a bis-Suzuki coupling of a β,β-dibromodehydroalanine with the corresponding heteroarylboronic acids. The absorption and fluorescence properties of the new tetracyclic compounds were studied in different solvents and in the presence of salmon sperm DNA. The results in several solvents show that either BTIN or BFIN can be used as fluorescence solvent sensitive probes. Spectroscopic studies of their interaction with dsDNA allowed to determine binding constant (K_i) values and binding site sizes (n). Fluorescence quenching experiments using iodide ion showed that intercalation is the preferred mode of binding to DNA. From the results obtained, BTIN is the more intercalative compound and has a higher affinity to DNA. The interaction of BTIN with DNA was also studied electrochemically, by using differential pulse voltammetry (DPV) in connection with disposable pencil graphite electrode (PGE). After the interaction of BTIN with DNA, the oxidation signals of BTIN and adenine strongly decreased. The latter result was attributed to the binding of BTIN to DNA and the former points to a possible damage of the oxidizable groups of BTIN after intercalation into DNA. The results of spectroscopic and electrochemical studies of BTIN interaction with DNA are in good agreement.