{[(2R,3R,4S,5S)-2-(6-Amino-9H-purin-9-yl)-5-[({[({[(2S,3R,4R,5R)-5-(3-carbamoyl-1,4-dihydropyridin-1-yl)-3,4-dihydroxyoxolan-2-yl]methoxy}(hydroxy)phosphoryl)oxy](hydroxy)phosphoryl}oxy)methyl]-4-hydroxyoxolan-3-yl]oxy}phosphonic Acid