Synthesis and redox-active base-pairing properties of DNA incorporating mercapto C-nucleosides

Here, we describe the synthesis and incorporation of the nucleoside base analogue C-deoxyribonucleoside carrying thiophenol into DNA. The 1′-β compound was synthesized by Friedel–Crafts alkylation, followed by deprotection. The coupling reaction with 3,5-ditoluoyl-1-α/β-methoxy-2-deoxy-d-ribose and diphenyldisulfide in the presence of SnCl4 afforded the α/β mixture (β/α=2.8), and the β-form was separated by silica gel chromatography. After formation of the phosphoramidite derivative, the C-nucleoside was incorporated into DNA. When the mercapto-bases were incorporated into complementary singled-stranded (ss) DNAs, the resulting duplex displayed high thermal stabilization on treatment with bubbling O2 (Tm 73 °C), but was destabilized in the presence of mercaptoethanol (Tm 33 °C). CD spectra showed that the duplex had a right-handed double-stranded structure. Imino proton NMR studies of temperature stability suggested that the strength of hydrogen bonding around the mercapto C-nucleoside was larger when treated with bubbling O2 than when in treated with reducing agent. Thus, formation of the base-to-base disulfide bond increased the stability of the duplex; correspondingly, reduction of the disulfide to two thiol bases destabilized the DNA reversibly. The duplex-forming disulfide base pair showed resistance to exonulease . The present strategy could be used to introduce new functionalities into cells and novel biomaterials.