N6-[1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-3-O-[[bis(1-methylethyl)amino](2-cyanoethoxy)phosphino]-2-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-1,4-dihydro-4-oxo-2-pyrimidinyl]-N2-[[2-(trimethylsilyl)ethoxy]carbonyl]-L-lysine 2-(trimethylsilyl)ethyl ester