Crystal and molecular structure of a hydrogen-bonded complex containing adenine and hypoxanthine derivatives: 9-Ethyl-8-bromoadenine-9-ethyl-8-bromohypoxanthine

Abstract

9-Ethyl-8-bromoadenine and 9-ethyl-8-bromohypoxanthine form a 1:1 hydrogen-bonded complex in the crystalline state. The structure has been determined by three-dimensional X-ray diffraction methods and refined by block diagonal least squares to a final residual of 9.1%. The crystals are triclinic, space group P 1 ̄ , with a = 8.55 A ̊ , b = 7.23 A ̊ , c = 14.65 A ̊ , α = 87 ° 8′, β = 102 ° 34′ and γ = 92 ° 25′ . The adenine and hypoxanthine bases form a planar complex, joined by two hydrogen bonds; an N-H…N bond involving N(1) of hypoxanthine and N(7) of adenine, and an N-H…O bond involving the amino group of adenine and the carbonyl oxygen of hypoxanthine. The over-all crystal structure is a sheet-like structure, in which adjacent base pairs are related by a center of symmetry and are connected by hydrogen bonds between the adenine residues. The possible significance of this structure to Crick's “wobble” hypothesis is discussed.