4-Amino-8-[3-(4-{3-[4-azido-5-(hydroxymethyl)oxolan-2-yl]-5-methyl-2,6-dioxo(1,3-dihydropyrimidinyl)}but-2-ynyl)-5-methyl-2,4-dioxo(1,3-dihydropyrimidinyl)]-1,7-dioxa-9-(1,1,2,2-tetramethyl-1-silapropoxy)-6-[(1,1,2,2-tetramethyl-1-silapropoxy)methyl]-2-thiaspiro[4.4]non-3-ene-2,2-dione AIDS-122975 AIDS122975