[5-(6-aminopurin-9-yl)-4-hydroxy-2-[[hydroxy-[hydroxy-[3-hydroxy-3-[2-[2-(3-hydroxybutanoylsulfanyl)ethylcarbamoyl]ethylcarbamoyl]-2,2-dimethyl-propoxy]-phosphoryl]oxy-phosphoryl]oxymethyl]oxolan-3-yl]oxyphosphonic acid