Structure of a potassium salt of Lasalocid A and an investigation of solid–state conformational variance of the Lasalocid A backbone in known complexes

Abstract

The structure of a potassium salt of the polyether ionophore antibiotic Lasalocid A has been determined by single–crystal X–ray crystallography. A dimeric structure is revealed in which two antibiotic molecules present hemispheric oxygen co–ordination environments for two potassium centres. Co–ordination for both cations is further fulfilled by contact with the oxygen atoms of two discrete dimethylformamide molecules that bridge the two potassium centres. Close analysis using directional statistics of the conformation of the backbone of the Lasalocid A molecule in all previously reported crystal structures, as well as the potassium salt reported here, reveals that conformation is substantially conserved throughout the series, aside from some variation in the twist of the carboxylate group with respect to the plane of the aromatic ring, and the orientation of the tetrahydrofuran ring. The Lasalocid A molecule in the potassium complex presented here is the closest fit to the averaged Lasalocid structure, derived from the family of known complexes,