Nucleosides and Nucleotides. Part 207: Studies in the Chemical Conversion of the 4-Carboxamide Group of 5-Amino-1-β-d-ribofuranosylimidazole-4-carboxamide (AICA-Riboside). Application for the Synthesis of 1-Deazaguanosine

A mild and versatile chemical conversion of the 4-carboxamide group of 5-amino-1-β-d-ribofuranosylimidazole-4-carboxamide (AICA-riboside) is described. The reaction of protected AICA-riboside with di-tert-butyl dicarbonate gave 5-[N,N-di-(tert-butoxycarbonyl)]amino-1-(5-O-tert-butyldimethylsilyl-2,3-O-isopropylidene-β-d-ribofuranosyl)imidazole-4-[N,N-di-(tert-butoxycarbonyl)]carboxamide in 71% yield. The resulting tetraBoc derivative was treated with sodium methoxide, benzylamine, or acetonitrile anion to give the corresponding methyl ester, N-benzylcarboxamide, or cyanoacetyl products. The 4-cyanoacetylimidazole derivative was converted into 1-deazaguanosine via an intramolecular cyclization.