Solid-phase stereoselective synthesis of 2′-O-methyl-oligoribonucleoside phosphorothioates using nucleoside bicyclic oxazaphospholidines

The use of 2′-OMe-ribonucleoside bicyclic oxazaphospholidines derived from (R)- or (S)-2-pyrrolidinemethanol has enabled the stereoselective synthesis of (Rp)-, and (Sp)-2′-O-methyloligoribonucleoside phosphorothioates. Interestingly, higher stereoselectivity (96–98%) was observed in the synthesis of (Sp)-2′-O-methyl-oligoribonucleoside phosphorothioates compared to that in the case of (Sp)-oligodeoxyribonucleoside phosphorothioates (90%).