Novel synthetic approach to asymmetric monocationic trimethine cyanine dyes derived from N-ethyl quinolinum moiety. Combined fluorescent and ICD probes for AT-DNA labelling

Two asymmetric monocationic trimethine cyanine dyes were obtained via condensation reaction between 2-methylbenzothialolium salts containing various (aliphatic and benzyl) substituents on the nitrogen atom of the benzothiazolic chromophore, and 1-ethyl 4-(2-(phenylamine)vinyl)quinolin 1-ium iodide, by a novel improved method at room temperature under mild conditions. Both compounds bind non-covalently to double stranded DNA and RNA by micromolar affinity, but give highly selective fluorescent response > 650 nm for only AT-DNA sequences at excess of DNA over dye, combined with equally AT-DNA selective ICD response at dye/DNA crowded conditions (r([dye]/[AT-DNA]) > 02)-namely ICD bands (attributed to dye-dimer formation) allow determination of AT-DNA at submicromolar concentrations. Selectivity was attributed to particular steric properties of AT-DNA minor groove in respect to other studied ds-DNA/RNA. Comparison of aliphatic- and benzyl- dye showed that only aliphatic- derivative revealed ICD band upon binding to AU-RNA major groove and short AT-sequences in mixed sequence (ct-)DNA. (C) 2016 Elsevier B.V. All rights reserved.