1-[5-[[[5-(2-amino-6-oxo-1H-purin-9-yl)-2-[[[5-(2-amino-6-oxo-1H-purin-9-yl)-2-[[[5-(2-amino-6-oxo-1H-purin-9-yl)-2-[[[5-(2-amino-6-oxo-1H-purin-9-yl)-2-[[hydroxy-[2-(hydroxymethyl)-5-(5-methyl-2,4-dioxopyrimidin-1-yl)oxolan-3-yl]oxyphosphinothioyl]oxymethyl]oxolan-3-yl]oxy-hydroxyphosphinothioyl]oxymethyl]oxolan-3-yl]oxy-hydroxyphosphinothioyl]oxymethyl]oxolan-3-yl]oxy-hydroxyphosphinothioyl]oxymethyl]oxolan-3-yl]oxy-hydroxyphosphinothioyl]oxymethyl]-4-hydroxyoxolan-2-yl]-5-methylpyrimidine-2,4-dione