Asymmetric organocatalytic synthesis of dinucleoside phosphorothioates. Towards antisense therapy

Abstract

Phosphorothioate oligonucleotides have been deeply studied as antisense therapy drugs. Their stereoselective synthesis, however, still depends on the use of chiral auxiliaries or modifications on the individual nucleosides, which slow their synthesis and increase costs. A catalytic asymmetric synthesis of these oligonucleotides would therefore be of great interest. Herein the catalytic asymmetric synthesis of dinucleoside phosphorothioates is attempted. After failing to optimise the conditions for the coupling using 4-DMAP-N-oxides as nucleophilic catalysts, hydrogen bond donors were envisaged as potential catalysts. Through the use of bifunctional thioureas containing a tethered amine, adequate conditions for the coupling were found and diastereoselectivity could be measured. Although low conversions were obtained, moderate selectivities were achieved for the synthesis of these dinucleosides