Acetic acid (2R,3S,5R)-2-{4-[(2S,3R,5R)-2-formyl-5-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-tetrahydro-furan-3-yl]-3-oxo-butyl}-5-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-tetrahydro-furan-3-yl ester

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

3'-O-Acetyl-5'-{3-[(3'R)-5'-(4,4'-dimethoxytrityl)-3'-deoxythymidin-3'-yl]-2-oxopropyl}-5'-deoxythymidine