Fluorescent nucleobase analogs (FBAs) are widely used probes for nucleic acid analysis. In this study, we designed, synthesized, and investigated fluorescent 7-arylethenyl-7-deazaguanosine derivatives as novel FBAs conjugated to molecular rotor structures. More than 10 types of oligonucleotides (ONs) containing the designed FBAs were constructed via the postsynthetic modification of 7-iodo-7-deazaguanosine using Suzuki-Miyaura cross-coupling. This approach allowed the efficient construction of a guanosine-type FBA library. The duplex stability of ONs containing 7-arylethenyl-7-deazaguanosine was slightly lower than that of canonical ONs. In contrast, naphthylethenyl-modified derivatives unexpectedly showed enhanced triplex stability compared with canonical DNA triplexes. The synthesized FBAs exhibited fluorescence emissions in the visible region, and the fluorescence spectra of the duplexes and triplexes containing 7-arylethenyl-7-deazaguanosine exhibited enhanced emissions, which varied depending on the aryl substituent. In particular, upon G·TA triplex formation, 1-or 2-naphthylethenyl-modified derivatives acted as a molecular rotor and showed strong fluorescence enhancement in a sequence-selective manner.
Kawaguchi et al. (Tue,) studied this question.
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