Abstract
As a model compound for the interaction of tryptophan with nucleic acid bases, uracil and adenine, (uracil-1-ylethyl) (adenin-9-ylethyl) tryptophan dipeptide has been synthesized, and its molecular and crystal structure has been analyzed by the X-ray diffraction method. The crystal data are a=4.989 (2), b=30.056 (5), c=9.939 (1) Å, β=94.61 (3) °, Z=2, Dm=1.345 (1) g·cm-3, space group P21. The molecule takes a W-shaped extended conformation, and is linked with the neighboring molecule in a head-to-tail fashion through a reverse Watson-Crick base pairing. Consequently the molecules form an infinite chain along the b-axis. A weak stacking interaction is observed between the indole ring and the uracil base : the dihedral angle between them is 28.6 (3) °, and the average interplanar spacing is 3.95 Å. This stacking mode is formed by the dipole-dipole coupling between the respective aromatic rings.The result may indicate a possible access mode of a tryptophan residue to the uracil base of a single-stranded nucleic acid.
