The Crystal and Molecular Structure of a Derivative of 1,N⁶-Ethenoadenosine Hydrochloride. Dimensions and Molecular Interactions of the Fluorescent ϵ-Adenosine (ϵ Ado) System

The crystal structure of 7-ethyl-3-β-D-ribofuranosylimidazo[2,1-i]purine hydrochloride monohydrate (3) has been determined both to establish the direction of addition of chloroacetaldehyde to adenine in the preparation of ϵ-adenine derivatives and to probe the molecular interactions of the highly fluorescent e-adenosine derivative. The crystals of 3 are monoclinic, with a = 12.952 (3), b = 6.667 (2), and c = 9.679 (2) Å, and β = 101° 34′ (1′). There are two molecules of C₁₄H₁₈N₅O₄+Cl^-·H₂O in the space group P2₁. The structure has been refined to an R factor of 0.043 in 1373 nonzero reflections. The entire ϵ-adenine moiety is near-planar with a maximum deviation of 0.028 Å among the ring atoms. There are some minor differences in bond lengths in the adenine residue in 3 when compared to unbridged adenine rings, but the greatest differences involve the exocyclic angles at C(6). The arrangement about the glycosyl bond is syn (χCN = −109.1°) and the ribose ring exists in the C(2′) endo-C(1′) exo conformation. The C(4′)-C(5′)exocyclic bond is in the trans-gauche arrangement. The N-H bond in the base, all three O-H bonds in the sugar, and the water molecules are involved in hydrogen bonding in the monohydrate. The crystal can be divided into successive regions (in the a direction) of polar and nonpolar character. In the nonpolar regions, there are infinite stacks (in the b direction) of ϵ-adenine rings, each of which overlap considerably with their neighbors with alternate ring-ring separations of 3.344 and 3.324 Å. These overlaps are compared with those found in related molecules.