THE PRO-OLIGONUCLEOTIDE APPROACH - SOLID-PHASE SYNTHESIS AND PRELIMINARY EVALUATION OF MODEL PRO-DODECATHYMIDYLATES

A modified phosphoramidite method has been designed for the solid-phas e synthesis of two dodecathymidine phosphotriesters and two dodecathym idine thiono-phosphotriesters. In these analogs, each internucleoside link bears an S-acyl-2-thioethyl (Me-SATE or tBu-SATE) group removable upon esterase activation. Efficient synthesis of these lipophilic ana logs was achieved thanks to the use of a photolabile linker anchored t o the solid support in combination with thymidine-3'-O-phosphoramidite s having a SATE group in place of the regular 2-cyanoethyl one, Both d odecathymidine phosphotriester and thionophosphotriester having S-acet yl-2-thioethyl groups were found to be stable in the presence of snake venom and calf spleen phosphodiesterases whereas, upon incubation in CEM cell extracts, they were selectively hydrolyzed to the anionic par ent dodecathymidylate and dodecathymidine phosphorothioate, respective ly, In addition, Me-SATE-protected dodecathymidine thionophosphotriest er was stable in mouse and human sera as well as in human gastric juic e, These results depict the potential of SATE-protected oligonucleotid es as prodrugs of antisense oligonucleotides.