9H-fluoren-9-ylmethyl N-[4-[[9-[5-[[[2-[[bis(4-methoxyphenyl)-phenylmethoxy]methyl]-5-[6-[[4-[(4-methylpentanoylamino)methyl]benzoyl]amino]purin-9-yl]oxolan-3-yl]oxy-(2-cyanoethoxy)phosphanyl]oxymethyl]-4-[but-3-ynoxy-[di(propan-2-yl)amino]phosphanyl]oxyoxolan-2-yl]purin-6-yl]amino]-4-oxobutyl]-N-methylcarbamate