Purification of saponins from leaves of Panax notoginseng using preparative two-dimensional reversed-phase liquid chromatography/hydrophilic interaction chromatography

Abstract

Saponins are widely distributed in the plant kingdom and have been shown to be active components of many medicinal herbs. In this study, a two-dimensional purification method based on reversed-phase liquid chromatography coupled with hydrophilic interaction liquid chromatography was successfully applied to purify saponins from leaves of Panax notoginseng. Nine saponin reference standards were used to test the separation modes and columns. The standards could not be resolved using C18 columns owing to their limited polar selectivity. However, they were completely separated on a XAmide column in hydrophilic interaction liquid chromatography mode, including two pairs of standards that were coeluted on a C18 column. The elution order of the standards on the two columns was sufficiently different, with a correlation coefficient between retention times on the C18 and XAmide columns of 0.0126, indicating good column orthogonality. Therefore, the first-dimension preparation was performed on a C18 column, followed by a XAmide column that was used to separate the fractions in the second dimension. Fifty-four fractions were prepared in the first dimension, with 25 fractions rich in saponins. Eight saponins, including two pairs of isomeric saponins and one new saponin, were isolated and identified from three representative fractions. This procedure was shown to be an effective approach for the preparative isolation and purification of saponins from leaves of P. notoginseng. Moreover, this method could possibly be employed in the purification of low-content and novel active saponins from natural products.