8,8-Dimethyl-3-((5-(5-methyl-2,4-dioxo-3,4-dihydro-1(2H)-pyrimidinyl)tetrahydro-2-furanyl)methoxy)-3-oxido-7-oxo-2,4,6-trioxa-3-phosphanon-1-yl pivalate AIDS-149881 AIDS149881 NSC685578