[(2r,3s,4r,5r)-5-(2-amino-6-oxo-3,6-dihydro-9h-purin-9-yl)-3,4-dihydroxytetrahydro-2-furanyl]methyl (2r,3r,4r,5r)-2-(4-amino-2-oxo-1(2h)-pyrimidinyl)-4-hydroxy-5-(hydroxymethyl)tetrahydro-3-furanyl hydrogen (r)-phosphate