X-ray, spectroscopic and semiempirical investigation of the structure of lasalocid 6-bromohexyl ester and its complexes with alkali metal cations

The ionophoric antibiotic lasalocid acid has been converted to a novel 6-bromohexyl ester (LASBR) and its structure has been determined in the crystal by X-ray diffraction and in solution by NMR and FT-IR methods. In the crystal two symmetry-independent LASBR molecules are present. The structure of LASBR in solution is slightly different because the strongest intramolecular C(1)O⋯H(3)O hydrogen bond in the pseudo-aromatic ring becomes partially broken and a new hydrogen bond between O(4)H and carbonyl group C(13)O is formed. LASBR forms complexes with Li+, Na+ and K+ cations of exclusively 1:1 stoichiometry. The structures of complexes have been studied and visualized using semi-empirical calculation based on results of spectrometric and spectroscopic investigation. It is demonstrated that in contrast to lasalocid acid the novel ester forms preferential complexes with Li+ cation.