1-[4-Amino-9-(Tert-butyl-dimethyl-silanyloxy)-6-(tert-butyl-dimethyl-silanyloxymethyl)-3-nitro-2,2-dioxo-1,7-dioxa-thia-spiro[4.4]non-3-en-8-yl]-3,5-dimethyl-1H-pyrimidine-2,4-dione AIDS-112335 AIDS112335