摘要:
5-O-tert-Butyldimethylsiyl-1,2-O-isopropylidene-3(R)-(nicotinamid-2-ylmethyl)-alpha-D-ribofuranose (11a) and -3(R)-(nicotinamid-6-ylmethyl)-alpha-D-ribofuranose (11b) were prepared by condensation of 5-O-terr-butyldimethylsilyl-1,2-O-isopropylidene-alpha-D-erythro-3-pentulofuranose (10) with lithiated (LDA) 2-methylnicotinamide and 6-methylnicotinamide, respectively, and then deprotected to give 1,2-O-isopropylidene-3-(R)-(nicotinamid-2-ylmethyl)-alpha-D- ribofuranose(12a)and1,2-O-isopropylidene3(R)-(nicotinamid-6-ylmethyl)-alpha-D-ribofuranose (12b). Benzoylation as well as phosphorylation of compounds 12 afforded the corresponding 5-O-benzoate (13b) and 5-O-monophosphates (14a and 14b). Treatment of 13b with CF3COOH/H2O caused 1,2-de-O-isopropylidenation with simultaneous cyclization to the corresponding methylene-bridged cyclic nucleoside - 3',6-methylene-1-(5-O-benzoyl-beta-D-ribofuranose)-3-carboxamidopyridinium trifluoro-acetate (8b) - restricted to the ''anti'' conformation. In a similar manner compounds 14a and 14b were converted into conformationally restricted 2,3'-methylene-1-(beta-D-ribofuranose)-3-carboxamidopyridinium-5'- monophosphate (9a - ''syn'') and 3',6-methylene-1-(beta-D-ribofuranose)-3-carboxamido - pyridinium-5'monophosphate (9b - ''anti'') respectively. Coupling of derivatives 12a and 12b with the adenosine 5'-methylenediphosphonate (16) afforded the corresponding dinucleotides 17. Upon acidic 1,2-de-O-isopropylidenation of 17b, the conformationally restricted P-1-[6,3'-methylene-1-(beta-D-ribofuranos-5-yl)-3-carboxamidopyridinium]-P-2-(adenosin-5'-yl)methylenediphosphonate 18b -''anti'' was formed. Compound 18b was found to be unstable. Upon addition of water 18b was converted into the anomeric mixture of acyclic dinucleotides, i.e. P-1-[3(R)-nicotinamid-6-ylmethyl-D-ribofuranos-5-yl]-P-2-(adenosin-5'-yl)-methylenediphosphonate (19b). In a similar manner, treatment of 17a with CF2COOH/H2O and HPLC purification afforded the corresponding dinucleotide 19a.