The crystal and molecular structure of adenosine hydrochloride

The crystal structure of adenosine hydrochloride (C₁₀H₁₃N₅O₄.HCl) has been determined using three-dimensional intensity data collected on a four-circle diffractometer. The crystal is monoclinic, space group P2₁. There are two molecules in the unit cell of dimensions a = 6.647 ± 0.003, b = 16.739 ± 0.005, c = 6.397 ± 0.002 Å and β = 114°54′ ± 4′. The structure was solved by the heavy-atom method and refined by the method of block-diagonal least squares. The final R value is 0.037 for 1895 observed reflexions including those of zero intensity. Adenosine is protonated at N(1) in the crystal. The purine ring is almost exactly planar. In comparison with the structure of the non-protonated adenosine molecule reported by Lai & Marsh [Acta Cryst. (1972). B28, 1982–1989] significant differences have been found in four bond lengths and three bond angles in the purine ring. The dihedral angle between the least-squares planes of the base and the ribose is 107.9° and the glycosidic torsional angle, φ_CN, is −43°. The ribose ring is in the C(2′)-endo–C(3′)-exo conformation, and the C(2′) atom is displaced by 0.60 Å from the least-squares plane of the remaining four ring atoms. The orientation of the C(5′)—O(5′) bond is gauche with respect to the bonds C(4′)—O(1′) and C(4′)—C(3′).