P-(2-cyano-ethyl)-thymidylyl-(3'->5')-O3'-acetyl-thymidine

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