2,2-Dimethyl-propionic acid 2-{[2-(2,2-dimethylpropanoyloxy)ethylsulfanyl]-[5-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-2,5-dihydrofuran-2-ylmethoxy]phosphorylsulfanyl}ethyl ester AIDS-072926 AIDS072926 UA 644 tBu(iso)SATE d4T