Crystal Structure of N-Acetylkynurenine

Abstract

The crystal structure of N-acetylkynurenine [o-NH₂C₆H₄COCH₂CH(COOH)NHCOCH₃] was determined by direct methods. The crystals are monoclinic, a 11.200(2), b 9.708(1), c 11.451(1) Å,β 90.16(2)º, space group P2₁, with Z 4. The structure was refined by least squares to R 0.033 with 1909 unique reflections, collected on an automated four-circle diffractometer. The structure is similar to the related L-trytophan hydrochloride. The two molecules in the asymmetric unit (A,B) are generally similar structurally but differ slightly in the conformation of the N-acetyl chain which has dihedral angles with the plane of the benzene ring of 78.0º (A) and 81.5º (B). Torsion angles about the C(α)-C(β) bond between C(γ) and both the carboxyl and the amino groups make them mutually gauche. There is an extensive hydrogen-bonding system between the two distinct molecules and between similar molecules either to form a dimer or a linear polymer.