Novel fluorine-substituted deaza analogues of 5-azacytidine (AZC) and 5-aza-2'-deoxycytidine (dAZC) (3-deazacytosines) have been synthesized and tested for antitumor activity. Thus, 4-amino-3,5-difluoro-1-beta-D-ribofuranosyl-2(1H)-pyridinone (16), 4-amino-3-fluoro-1-beta-D-ribofuranosyl-2(1H)-pyridinone (17), 4-amino-5-fluoro-1-beta-D-ribofuranosyl-2(1H)-pyridinone (18), 4-amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)-3,5-difluoro-2 (1H)-pyridinone (25), 4-amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)-3-fluoro-2(1H)-pyridin one (26) 4-amino-1-(2-deoxy-alpha-D-erythro-pentofuranosyl)-3,5-difluoro-2(1H)-++ +pyridinon e (27), and 4-amino-1-(2-deoxy-alpha-D-erythro-pentofuranosyl)-3-fluoro-2 (1H)-pyridinone (28) were prepared by standard glycosylation procedures. Requisite heterocycle 4-amino-3,5-difluoro-2(1H)-pyridinone (6) was prepared in five steps from pentafluoropyridine (1). Other requisite fluoro heterocycles, 4-amino-3-fluoro-2(1H)-pyridinone (7) and 4-amino-5-fluoro-2(1H)-pyridinone (8), were obtained from a bis-defluorination of 4-amino-3,5,6-trifluoro-2(1H)-pyridinone (3) with hydrazine. Acetylation of 17 provided 4-amino-3-fluoro-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)-2(1H)-pyrid inone (29). Structure proof of target nucleosides and heterocyclic compounds was provided by X-ray diffraction, 19F and 1H NMR, and UV. The ID50 values of fluorine-substituted 3-deazacytosines and 3-deazacytidines were greater than 1 X 10(-5) M in L1210 lymphoid leukemia cells in culture. Nucleoside 17 and its tri- and tetraacetates were the most active compounds with ID50 values of 1.07 X 10(-5), 1.23 X 10(-5), and 1.25 X 10(-5) M, respectively. The target nucleosides and intermediate heterocycles were inactive against P388 and L1210 lymphocytic leukemia in mice, except nucleoside 17 (NSC-378066) and its triacetate 29 (NSC-382021). Nucleoside 17 exhibited confirmed DN2 activity (% T/C 169-230) at five dose levels (25-300 mg/kg). Prodrug 29 exhibited similarly confirmed L1210 in vivo activity.