7- Chloro pyridine glycosylation

N-3 (78JMC112). Treatment of 7-chloro-l-(tri-0-acetyl-/3-D-ribofuranosyl)imidazo[4,5-f>]pyridine with tetra-O-acetyl-D-ribofuranose and HgBr2 produced the 3-isomer in 75.9% yield with the indication that transglycosylation proceeds through the l,3-bis(glycosyl) intermediate to the thermodynamically more stable 3-isomer (82Mi4iooi), confirming the relative stabilites mentioned above. 

An interesting synthesis of these C-nucleosides utilized the easily accessible 5-(j3-D-ribofuranosyl)tetrazoles 235 as masked C-glycosyl-diazometh-ane. Reacting 235 with 2-chloro-3-nitropyridine gave a mixture of 1,2,4-triazolo[4,3-fl]pyridin-3-yl (236) and l,2,4-triazolo[l,5-a]pyridin-2-yl (237) C-nucleosides. The latter (237) resulted from thermally induced Dimroth-like rearrangement of the former (236) (86MI9) (Scheme 70). Compounds 236 and 237 possess considerable cytotoxic effect (86MI9). 

Chloro-, Bromo- and lodo-sugars. - The preparation of glycosyl halides and their use in the solid-phase synthesis of oligosaccharides has been reviewed/ A new method for the preparation of glycosyl chlorides involves the treatment of otherwise protected free sugars with triphosgene in the presence of pyridine/ ... 

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