Conformation and conformational exchange of Olopatadine hydrochloride

Besides the assignments of the 13C and 1H shifts by 1D and 2D NMR, the experiment 1H spectra of Olopatadine hydrochloride were recorded at temperature range 228–338 K. The variable-temperature spectra revealed a dynamic NMR effect which is attributed to conformational interconversion of the drug. At low temperature, the solution was shown to contain two conformers and the ration of them was 1:1. A conformational process with a free energy of activation of 56.7 kJ mol−1, coalescence temperature 298 K, was interpreted as geminal 1H exchange. Using molecule simulation, conformational candidates for two conformers are proposed.