Stereocontrolled Synthesis of Boranophosphate DNA by an Oxazaphospholidine Approach and Evaluation of Its Properties

In this paper, we describe the first stereocontrolled synthesis and properties of boranophosphate DNA (PB-DNA), which contains all of the four nucleobases longer than 10mer. Synthesis was accomplished via an oxazaphospholidine approach combined with acid-labile protecting groups on nucleobases. It was demonstrated that there were significant differences between all-(Rp)- and all-(Sp)-PB-DNA in terms of the duplex-formation ability, nuclease resistance, and ribonuclease H (RNase H) activity. In particular, all-(Sp)-PB-DNA was demonstrated to show a duplex-formation ability with RNA and RNase H activity, both of which are necessary for antisense-type nucleic acid therapeutics.