9H-fluoren-9-ylmethyl N-[4-[[9-[4-[2-aminoethoxy-[di(propan-2-yl)amino]phosphanyl]oxy-5-[[[2-[[bis(4-methoxyphenyl)-phenylmethoxy]methyl]-5-[6-[[4-[[[2-[4-[9H-fluoren-9-ylmethoxycarbonyl(methyl)amino]-1-hydroxybutoxy]acetyl]amino]methyl]benzoyl]amino]purin-9-yl]oxolan-3-yl]oxy-(2-cyanoethoxy)phosphanyl]oxymethyl]oxolan-2-yl]-6-hydroxy-1,6-dihydropurin-2-yl]amino]-4-oxobutyl]-N-methylcarbamate