Analytical and semi-preparative separation of diastereomeric lipid amino acid conjugates.

A series of biologically active peptides and their conjugates with lipidic amino acids were investigated by systematic change of the mobile phase composition using traditional octadecylsilica stationary phase and the newly developed Supelcosil LC-ABZ column. The mobile phases contained various concentrations of methanol and acetonitrile combined with 0.1% trifluoroacetic acid (TFA). Better peak shapes and higher resolution of the isomers could be observed when the mobile phase contained 0.1% TFA. More symmetrical peaks and much higher S values (slope of the log k' vs organic phase concentration plots) were obtained on the special reversed-phase column developed for anionic, basic or zwitterionic compounds. The optimum separation conditions were scaled up to a semi-preparative reversed-phase column (15 mm i.d.) to collect mg quantities of isomers for further studies.