1-[4-Amino-6,9-bis-(tert-butyl-dimethyl-silanyloxy)-2,2-dioxo-1,7-dioxa-2.lambda.-thia-spiro[4.4]non-3-en-8-yl]-5-methyl-3-(2-methyl-propenyl)-1H-pyrimidine-2,4-dione AIDS-105015 AIDS105015