[(2R,4S,5R)-2-[[[(2R,4S,5R)-2-[[[(2R,4S,5R)-2-[[[(2R,4S,5R)-5-(6-benzamidopurin-9-yl)-2-[[2-cyanoethoxy-[(2R,4S,5R)-5-(2,6-dihydro-1,3-oxazin-3-yl)-4-[2-[hydroxy(dimethyl)silyl]-2-methylpropyl]-2-(hydroxymethyl)oxolan-3-yl]oxyphosphoryl]oxymethyl]-4-[2-[hydroxy(dimethyl)silyl]-2-methylpropyl]oxolan-3-yl]oxy-(2-cyanoethoxy)phosphoryl]oxymethyl]-5-(2,3-dihydropyrrol-1-yl)-4-[2-[hydroxy(dimethyl)silyl]-2-methylpropyl]oxolan-3-yl]oxy-(2-cyanoethoxy)phosphoryl]oxymethyl]-4-[2-[hydroxy(dimethyl)silyl]-2-methylpropyl]-5-[2-(2-methylpropylamino)-6-oxo-1H-purin-9-yl]oxolan-3-yl]oxy-(2-cyanoethoxy)phosphoryl]oxymethyl]-5-(2,6-dihydro-1,3-oxazin-3-yl)-4-[2-[hydroxy(dimethyl)silyl]-2-methylpropyl]oxolan-3-yl] 4-oxopentanoate