(2R,5S)-5-(4-((((9-((2R)-2-((hydroxy(((isopropoxycarbonyl)oxy)methoxy)phosphoryl)methoxy)propyl)-9H-purin-6-yl)amino)methyl)amino)-2-oxopyrimidin-1(2H)-yl)-1,3-oxathiolane-2-carboxylic acid