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.