N-Benzoyl-5′-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxy-P-2-propen-1-yladenylyl-(3′→5′)-N-benzoyl-2′-deoxy-P-2-propen-1-yladenylyl-(3′→5′)-3′-O-[(1,1-dimethylethyl)dimethylsilyl]thymidine