7-Amino-1-(2-deoxy-β-erythro-pentofuranosyl)-1H-1,2,3-triazolo[4,5-d]pyrimidine: an 8-azaadenine nucleoside with the nucleobase in a syn conformation.

The title compound, C(9)H(12)N(6)O(3), shows a syn-glycosylic bond orientation [χ = 64.17 (16)°]. The 2'-deoxyfuranosyl moiety exhibits an unusual C1'-exo-O4'-endo ((1)T(0); S-type) sugar pucker, with P = 111.5 (1)° and τ(m) = 40.3 (1)°. The conformation at the exocyclic C4'-C5' bond is +sc (gauche), with γ = 64.4 (1)°. The two-dimensional hydrogen-bonded network is built from intermolecular N-H...O and O-H...N hydrogen bonds. An intramolecular bifurcated hydrogen bond, with an amino N-H group as hydrogen-bond donor and the ring and hydroxymethyl O atoms of the sugar moiety as acceptors, constrains the overall conformation of the nucleoside.