2-Propenoic acid, 3-[3-[(6R,8R,9R)-4-amino-9-[[(1,1-dimethylethyl)dimethylsilyl]oxy]-6-[[[(1,1-dimethylethyl)dimethylsilyl]oxy]methyl]-2,2-dioxido-1,7-dioxa-2-thiaspiro[4.4]non-3-en-8-yl]-3,6-dihydro-5-methyl-2,6-dioxo-1(2H)-pyrimidinyl]-, methyl ester, (2E)- AIDS-215981 AIDS215981 TSAO Deriv.