Chloro-Substituted Naphthyridine Derivative and Its Conjugate with Thiazole Orange for Highly Selective Fluorescence Sensing of an Orphan Cytosine in the AP Site-Containing Duplexes

Fluorescent probes with the binding selectivity to specific structures in DNAs or RNAs have gained much attention as useful tools for the study of nucleic acid functions. Here, chloro-substituted 2-amino-5,7-dimethyl-1,8-naphthyridine (ClNaph) was developed as a strong and highly selective binder for target orphan cytosine opposite an abasic (AP) site in the DNA duplexes. ClNaph was then conjugated with thiazole orange (TO) via an alkyl spacer (ClNaph–TO) to design a light-up probe for the detection of cytosine-related mutations in target DNA. In addition, we found the useful binding and fluorescence signaling of the ClNaph–TO conjugate to target C in AP site-containing DNA/RNA hybrid duplexes with a view toward sequence analysis of microRNAs.