C-NUCLEOSIDES .12. SYNTHESIS OF 2'-DEOXYPYRIDAZINONE C-NUCLEOSIDE FROM 2-(2,3,5-TRI-O-BENZOYL-BETA-D-RIBOFURANOSYL)FURAN

The versatile 2′-deoxy-β-D-ribofuranosyl-C-nucleoside precursor 4-(1,4-anhydro-3,5-di-O-benzoyl-2-deoxy-D-erythro-pentofuranosyl)-4-oxobutyric acid (4) can be obtained from the furanone (2) which was prepared from the glycosylfuran (1). The synthesis of 3-(2-deoxy-β-D-erytho-pentofuranosyl) pyridazin-6(1H)-one (12) from (4) is described. Catalytic hydrogenation of the γ-keto butenoic acid (3) afforded the γ-keto butyric acid (4) and its α isomer (5) in a 1:1 ratio. Treatment of ester (6) with hydrazine hydrate in methanol afforded the dihydropyridazinone (8) in 74% yield. Aromatization of compound (8) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone gave the pyridazinone (10) in 87% yield. Deprotection of compound (10) with methanolic sodium hydroxide afforded compound (12) in 77% yield.