O-[(2R,3S,4R,5R)-5-(2-amino-6-oxo-3,6-dihydro-9H-purin-9-yl)-2-({[(S)-({(2R,3S,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-4-hydroxy-2-[(thiophosphonooxy)methyl]tetrahydrofuran-3-yl}oxy)(sulfanyl)phosphoryl]oxy}methyl)-4-hydroxytetrahydrofuran-3-yl] dihydrogen (S)-phosphorothioate