Stereocontrolled synthesis of dinucleoside phosphorothioates using a fluorous tag

Dinucleoside phosphorothioates were synthesized in a stereocontrolled manner (diastereoselectivity > 99:1) by using thymidine derivatives bearing a simple perfluoroalkyl tag (C6F13 or C8F17) at the 3′-end and diastereopure nucleoside 3′-O-oxazaphospholidine monomers. Fluorous-tagged intermediates in the synthesis were easily purified by a simple fluorous solid-phase extraction process.