Nucleosid‐Synthesen in der Imidazolreihe

Synthesis of Imidazole Nucleosides The acid‐catalyzed fusion of dimethyl imidazole‐4,5‐dicarboxylate ( 7 ) with 1‐O‐acetyl‐2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranose ( 6 ) provided dimethyl 1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranosyl)imidazole‐4,5‐dicarboxylate ( 11 ) as the major product together with some β‐anomer ( 13 ). The β‐anomer ( 11 ) was obtained as the only product when the trimethylsilyl derivative ( 9 ) of 7 was condensed with 6 in the presence of stannic chloride. Nucleoside 11 was treated with ammonia, and various primary amines to provide 1‐β‐D‐ribofuranosylimidazole‐4, 5‐dicarbox‐amide ( 5 ) and N, N'‐disubstitued dicarboxamides ( 18‐26 ) respectively. The synthesis of 1‐β‐( 33 ) and 1‐β‐D‐arabinofuranosylimidazole‐4,5‐dicarboxamide ( 34 ), is also described. The conformation of 5 , as studied by 1 H‐and 13 C‐NMR.‐spectroscopy, was shown to be very similar to that of adenosine. The oxidation of the 2′,3′‐O′‐isopropylidene derivative ( 15 ) of 5 with potassium permanganate or chromic oxide, followed by deprotection, or the direct oxidation of 5 with oxygen in the presence of platinum catalyst, led to the corresponding 5′‐carboxylic acid 36 . This was further converted into esters ( 37 and 38 ) and amides ( 39‐42 ). Treatment of some nucleosides with fuming nitric acid in oleum at ‐ 30° yielded the nitric acid esters 43‐51 . Beside the nitration of their sugar residues, one of the imidazolecarboxamide functions in nucleosides 46‐51 and both N‐methyl‐carboxamide functions in 44 were nitrated. Finally, reaction of the N, N'‐dimethyl‐N, N'‐dinitrodicarboxamide 44 with alkyl‐ und aralkylamines, afforded the N, N'‐dialkyl‐and N, N'‐diaralkyldicarboxamides 52‐56 .