2-Cyanoethyl {5'-[3-((3'R)-3'-deoxythymidin-3'-yl)-2-oxopropyl]-5'-deoxythymidin-3'-yl}(3'-acetylthymidin-5'-O-yl)phosphinate

5'-{3-[(3'R)-5'-(4,4'-Dimethoxytrityl)-3'-deoxythymidin-3'-yl]-2-oxopropyl}-3'-O-[2-cyanoethoxy(diisopropylamino)phosphino]-5'-deoxythymidine