Solution conformation of lasalocid and lasalocid-Na+ (X-537A)

The complete unraveling of the proton nuclear magnetic resonance spectra at high field strength of Lasalocid (1) and its sodium salt (2) in different solvents allowed the definition of their solution conformations. The free acid, a lozengeshaped molecule of 17 × 13 × 9 Å is prefolded in a way almost identical to that of its sodium derivative, where the ion lies in the centre, surrounded by all the oxygen atoms in the molecule except for the phenolic one. Although the upper side of the molecule is rather accessible to hydrophilic approach, some alkyl substituents are arranged out- and upwards, thus shielding the ion from possible contact with lipophilic surroundings. The spatial picture suggests that the ion is trapped upon arrival at one side (the flat upper side) and is released either at the same or at the opposite side.