1,7-Dideaza-2 `-deoxy-6-nitronebularine: a pyrrolo[2,3-b]pyridine nucleoside with an intramolecular hydrogen bond stabilizing the syn conformation

Abstract

The title compound [systematic name: 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-4-nitro-1H-pyrrolo[2,3-b]pyr idine], C12H13N3O5, forms an intramolecular hydrogen bond between the pyridine N atom as acceptor and the 5'-hydroxy group of the sugar residue as donor. Consequently, the N-glycosylic bond exhibits a syn conformation, with a chi torsion angle of 61.6 (2)degrees, and the pentofuranosyl residue adopts a C2'-endo envelope conformation (E-2, S-type), with P = 162.1 (1)degrees and tau(m) = 36.2 (1)degrees. The orientation of the exocyclic C4'-C5' bond is sc (gauche, gauche), with a torsion angle gamma = 49.1 (2)degrees. The title nucleoside forms an ordered and stacked three-dimensional network. The pyrrole ring of one layer faces the pyridine ring of an adjacent layer. Additionally, intermolecular O-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds stabilize the crystal structure.