P-({[(2R,3S,4R,5R)-5-(2,4-dioxo-3H-pyrimidin-1-yl)-3,4-dihydroxytetrahydro-2-furyl]methyl}oxy)-P-({[({[({[(2R,3S,4R,5R)-5-(2,4-dioxo-3H-pyrimidin-1-yl)-3,4-dihydroxytetrahydro-2-furyl]methyl}oxy)oxido(oxo)-λ5-phosphanyl]oxy}oxido(oxo)-λ5-phosphanyl)oxy]oxido(oxo)-λ5-phosphanyl}oxy)phosphinate