(R)-{[(S)-{[(S)-{[(S)-([(2S,3R,4R,5R)-5-(6-amino-9H-purin-9-yl)-3,4-dihydroxyoxolan-2-yl]methyl phosphonato)]oxy}phosphinato]oxy}phosphinato]oxy}({[(S)-([(2S,3S,5S)-3-azido-5-(5-methyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-yl)oxolan-2-yl]methyl phosphonato)]oxy})phosphinate