An experimental charge density study of mesulergine hydrochloride,a dopamine agonist

Carefully measured high-resolution X-ray diffraction measurements at 120(2) K have been used to map the electron deformation density of mesulergine hydrochloride, a dopamine agonist. A total of 52,508 intensities were measured with MoK radiation to a sin/)_max = 0.84~Å^–1. Averaging symmetry equivalent reflections yielded 9,418 unique reflections. A least squares refinement procedure was used in which multipole parameters were added to describe the distortions of the atomic electron distributions from spherical symmetry. Maps of the model electron deformation density distribution show the distribution of electron density in mesulergine hydrochloride. Molecular electrostatic potentials have been calculated from the electron densities determined in the least-squares multipole refinement. A region of negative electrostatic potential near N23 in the NHSO₂N(CH₃)₂ substituent suggests that the nitrogen atom would be reactive toward electrophilic attack. Net atomic charges calculated from refined monopole population parameters yielded charges of +0.17 for the NHSO₂N(CH₃)₂ substituent and +0.37 for the ergoline fused ring system. There does not seem to be an area of the molecule that, based on the results of this study, is more electron rich or electron deficient than others. Crystallographic data: C₁₈H₂₆N₄O₂SHCl, P2₁, a = 12.1281(3) Å, b = 6.1357(4) Å, c = 13.5935(4) Å, = 105.14(5), V = 974.14(5) ų, Z = 2.