1-(2',3'-Dideoxy-2'-fluoro-.beta.-D-threo-pentofuranosyl)uracil 124424-25-5 2'F-dd-araU 2,4(1H,3H)-Pyrimidinedione, 1-(2,3-dideoxy-2-fluoro-.beta.-D-threo-pentofuranosyl) AIDS-001166 AIDS001166 NSC639425