1990 年 38 巻 4 号 p. 851-855
As a series in the structural studies of tryptophan metabolites by an X-ray diffraction method, the crystal and molecular structure of 6-hydroxymelatonin, one of the final tryptophan metabolites, has been determined. The space group is Pbca with cell dimensions a=9.309(1), b=12.061(1) and c=22.301(1)Å. The structure was refined to R=0.053 for 2108[|Fo|>0.0) observed reflections. In contrast to a nearly planar trans conformation of melatonin, a precursor of 6-hydroxymelatonin, a folded conformation of the N-acetylaminoethyl side chain to the indole ring was observed, which is also energetically stable as shown by quantum chemical modified neglect of diatomic overlap calculations for melatonin and 6-hydroxymelatonin molecules. The oxygen atom of 6-hydroxy group participates in two intermolecular hydrogen bond formations as an electron donor and an acceptor. Three-dimensional molecular packing is essentially stabilized by these and NH (indole)…O (acetyl) hydrogen bonds.
