Stereocontrolled Synthesis of Oligoribonucleoside Phosphorothioates by an Oxazaphospholidine Approach

Oligoribonucleoside phosphorothioates (PS-ORNs) stereodefined at the phosphorus atoms were synthesized on solid support. Thermal denaturating experiments of the resultant PS-ORNs showed that a backbone consisting of (Sp)-PS-linkages as well as stereorandom PS-linkages had an unexpectedly large destabilizing effect on a PS-ORN-ORN duplex, whereas a backbone consisting of (Rp)-PS-linkages slightly stabilized a duplex.