Triazole C-Nucleosides

Cycloaddition of C-jS-D-ribofuranosylalkynes (305) to benzyl azide [74JCS(P1)1943 75JCS(CC)501 77M15] or trimethylsilyl azide (76JOC84) 

The double-headed 1,2,4-triazole acyclo C-nucleosides 713 were obtained by cyclization of galactaroyl l,4-bis(4-arylthiosemicarbazide) acetates (712) 

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The chlorine atom of the pyrimidin-3-yl homo C-nucleoside 564 was displaced by azide ions followed by reduction of the introduced azido function to the amino compound 565. Treatment of the latter with nitrous acid formed the 1,2,3-triazole ring of the two l,2,3-triazolo[l,5-c]pyrimidin-... 

The term C-nucleoside was only coined after isolation and characterization of the first member of this class pseudouridine, in 1975 [97ACH(ip)]. Before that, alditolyl derivatives of some heterocycles (acyclo C-nucleo-sides) were known both as natural products (alditolyl pteridines or biopterins) as well as products of syntheses (e.g., alditolyl derivatives of imidazoles, benzimidazoles, thiazoles, benzothiazoles, 1,2,3-triazoles, quinoxalines, and flavazoles) and were classified as carbohydrate derivatives of heterocyclic compounds. After isolation of pseudouridine, other naturally occurring members were successively isolated, characterized, and synthesized. It is worth mentioning that synthesis preceded isolation in two cases 9-dea-zaadenosine and pyrrolosine. Comparison with the synthetic compounds facilitated structure elucidation in one case (9-deazaadenosine) and structure reassignment in the other (pyrrolosine). 

D-ga/acio-Pentitol-l-yl)-2-phenyl-l,2.3-triazole (655) underwent intramolecular cyclodehydration and concurrent O-4-toluenesulfonylation when treated with 4-toluenesulfonyl chloride to give the derivatized 1,2,3-triazole homo C-nucleosides 656-658 [95JCR(S)54] (Scheme 173). 

Hager, C. Miethchen, R. Reinke, H. Organofluorine compounds and fluorinating agents. Part 26. New reversed nucleosides—perfluoroalkyl substituted 1,2,3-triazoles linked to D-galactose and D-altrose. J. Fluorine Chem. 2000, 104, 135-142. 

C.B. Reese and A. Ubasawa, Reaction between l-arenesulphonyl-3-nitro-1,2,4-triazoles and nucleoside... 

The condensed 1,2,4-triazole ring of 577 was formed as a result of condensing the jS-D-ribofuranosylcarbodithioate 512 with 2-hydrazino-4-hydroxy-6-methylpyrimidine. Unlike the l,2,4-triazolo[l,5-c]pyrimidine analog 568, the l,2,4-triazolo[4,3-fl]pyrimidin-3-yl C-nucleoside 577 did not undergo Dimroth rearrangement (89MI5) (Scheme 154). 

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