Multiple peak formation in reversed-phase liquid chromatography of ramipril and ramiprilate

Abstract The chromatographic performance of ramipril, an angiotensin-converting enzyme inhibitor, and ramiprilate, its active metabolite, was studied on an octadecyl-bonded silica stationary phase and with aqueous eluents. The substances are peptide-related with a proline residue, a group of compounds known to exist as a mixture of two conformers in aqueous solution. The influence of column temperature, flow-rate, pH, organic modifier and stationary phase was investigated, and the cis and trans isomers of ramiprilate were assigned by nuclear magnetic resonance studies. Multiple and irregularly shaped chromatographic peaks were obtained, but by choosing appropriate conditions the compounds were eluted as single, symmetric peaks, or the two isomers of each compound could be separated.