1-[(2R,4S,5R)-4-[[(2R,3S,5R)-5-(2-amino-6-oxo-1H-purin-9-yl)-3-hydroxyoxolan-2-yl]methoxy-methylphosphoryl]oxy-5-[[[(2R,3S,5R)-5-(4-amino-2-oxopyrimidin-1-yl)-2-[[[(2R,3S,5R)-5-(4-amino-2-oxopyrimidin-1-yl)-2-[[bis(4-methoxyphenyl)-phenylmethoxy]methyl]oxolan-3-yl]oxy-methylphosphoryl]oxymethyl]oxolan-3-yl]oxy-methylphosphoryl]oxymethyl]oxolan-2-yl]-5-methylpyrimidine-2,4-dione