The Crystal and Molecular Structure of Kinamycin C p-Bromobenzoate

The molecular structure of kinamycin C has been determined by means of an X-ray study of its p-bromobenzoate derivative, C₃₁H₂₃N₂O₁₁Br. The crystals are monoclinic, P2₁, with four molecules of the derivative and four molecules of benzene in a unit cell of dimensions: a = 18.404 ± 0.005, b = 21.299 ± 0.004, c = 9.049 ± 0.001 Å, and β = 90.07 ± 0.03°. Reflection intensities were measured visually from equi-inclination Weissenberg photographs taken with Cu Ka radiation. The structure was solved by the heavy-atom method, and was refined by the block-diagonal-matrix least-squares method using anisotropic temperature factors for all the atoms. The final R factor is 8.9%. The stereostructures of the two crystallographically independent molecules are almost identical. The skeleton of the molecule is made up of four fused rings: two of these form a 1,4-naphthoquinone system and the rest are a pyrrole and a cyclohexene ring. A cyano group is bonded to the nitrogen atom of the pyrrole ring, which is rather unusual in an antibiotic.