(5S,9S,2R,6R,8R)-8-(2,4-Dioxo(1,3-dihydropyrimidinyl))-9-(1,1,2,2-tetramethyl-1-silapropoxy)-6-[(1,1,2,2-tetramethyl-1-silapropoxy)methyl]-7-oxa-4-thia-1-azaspiro[4.4]nonane-2-carboxylic acid AIDS-161505 AIDS161505 NSC699328