A series of ribofuranosyl-and 2-deoxyribofuranosyl homo-and spacered-C-nucleosides have been synthesized by reaction of fully protected 3-(1-deoxy-β-D-ribofuranosyl-1-yl)propanal (1), 3-(1,2-dideoxy-β-D-ribofuranos-1-yl)propanal (14), 1-(1-desoxy-β-D-ribofuranos-1-yl)pent-4-yn-3-on (19), 1-(1-desoxy-β-D-ribofuranos-1-yl)-5-phenyl-pent-4-yn-3-on (20), 1-(1,2-didesoxy-β-D-ribofuranos-1-yl)pent-4-yn-3-on (29), and 1-(1,2-didesoxy-β-D-ribofuranos-1-yl)-5-phenylpent-4-yn-3-on (30) with different nucleophiles. The preparation of 1 and 14 proceeds by Knoevenagel reaction with malononitrile, cyanoacetamide and 2-cyano-N-(4-methoxyphenyl)acetamide and subsequent cyclization with sulphur to thiophenes 5, 7, 8, 16 and then by cyclization with triethyl orthoformate to give thienopyrimidine 6 and thienopyrimidinone 9, 10, and 17. Treatment of acetylenic ketones 19, 20, 29, and 30 with acetamidinium chloride, benzamidinium chloride, and S-methylisothiouronium sulphate provided the corresponding pyrimidines 21-26, 31, 32. Finally, the use of 4H-1,2,4-triazol-3-amine and 2-aminobenzimidazole as 1,3-N,N'-dinucleophiles afforded the triazolopyrimidines 35, 39 and the pyrimidobenzimidazoles 36, 37, and 40, respectively. Deprotection of a selected number of Cnucleosides was achieved by one or two steps procedure without serious problems. That makes these C-nucleosides promising candidates for the synthesis of monomers suitable for solid phase nucleic acid oligomerization.
