Synthetic, structural, and conformational studies of methylated ring-expanded nucleosides containing the imidazo[4,5-e] [1, 4]diazepine ring system

Syntheses of 4- and 7-methyl 4, 5, 7, 8-tetrahydro-6H-3-(β-D-ribofuranosyl)imidazo[4, 5-e] [1, 4]diazepine-5, 8-dione, 3 and 4, respectively, are reported. Single-crystal X-ray diffraction analysis of the aglycon of 3 aided in confirming the site of methylation in 3, and that of 4 in elucidating the solid state conformation of 4. Solution conformations of 3 and 4, along with their parent nucleoside 1 and the latter's 1-glycosyl regioisomer 2, were investigated by NOE and CD measurements.