The elution behavior of cyclosporine congeners in a developed HPLC system reflects the lipophilicity.

Recently, the development of cyclic peptide drugs has accelerated. To develop an analytical method to determine the physicochemical properties of these lipophilic drug candidates, we investigated the separation mechanism of cyclosporine congeners A, B, C, and D using HPLC with a column packed with 2-μm nonporous octadecylsilyl silica particles at high temperature. The four congeners were eluted with good repeatability in terms of retention time, peak area, and theoretical plate number. A difference of one amino acid in the eleven amino-acid sequence of the cyclosporine congeners was able to be recognized by our system within 4 min by isocratic elution, and the resolution was greater than 1.68. The calculated logP values of these congeners were well correlated with the retention factors with a correlation coefficient of 0.991. We could elucidate the separation mechanism of cyclosporine congeners on the high-temperature HPLC system. These results show that this method using HPLC on a column packed with 2-μm nonporous octadecylsilyl silica particles can be used for studying the lipophilicity of cyclosporine congeners.