The solution structure of a lasalocid A metal complex in lipophilic solvents

Lasalocid A (LasNa), a common antibiotic in veterinary medicine, is a polyetheral ionophore, disrupting cation equilibria through the cell wall. By means of circular dichroism (in the UV and in the near-IR), paramagnetic NMR, and with the aid of the program PERSEUS, we determined the solution geometry of the 1:1 Las–Yb3+ complex in CD3CN and CDCl3, following a protocol similar to the one successfully used for the anthracycline–metal adduct. The resulting structure is in full agreement with the expectation of the ligand wrapping around the cation in a horseshoe shape. The oxygen atoms participate in the coordination either through a direct, first sphere, or a longer range interaction.

We describe the solution structure of the ionophore antibiotic lasalocid complexed to Yb(III), solved by means of paramagnetic NMR. Binding to the metal, lasalocid assumes a rigid wrapped horseshoe-shaped conformation. Structural identity between acetonitrile (where experiments are more easily carried out) and chloroform is verified, demonstrating that this structure is an excellent model for the role of Lasalocid as cation carrier through membranes.Figure optionsDownload as PowerPoint slide