Purification of two valepotriates from Centranthus ruber by centrifugal partition chromatography: From analytical to preparative scale

Abstract

Considering chemical complexity of plant crude extracts, purification of natural products is a rate limiting process to identify new compounds as well as to obtain standard references for quantitative or qualitative purposes. In the present work, a centrifugal partition chromatography (CPC) method was developed to isolate and produce high quality reference standards of valtrate and 7-homovaltrate from Centranthus ruber L. roots. These two compounds are controversial aglycon iridioids regulated by the legislation on plant-based dietary supplements. A new biphasic solvent system suitable for CPC separation of valepotriates was developed. It was composed of methanol/hexane/water (5/5/0.8, v/v/v). It yielded a partition coefficient near 1 and a theoretical selectivity of 1.3 between both targeted compounds. Optimization of CPC experimental parameters at the analytical scale (50 mL- and 100 mL-column capacity) enabled compounds’ separation with a flow rate of 8 mL/min at 2500 rpm. Then a scale up from a 100 mL-column capacity to a 1000 mL-column capacity has been studied using the “free-space between peaks” concept. It allowed an injected quantity 16 times higher in comparison to the maximal loading capacity of the 100 mL-column. Both valtrate and 7-homovaltrate were recovered in one single step with a purity over 97%. Further MS and NMR characterization allowed to confirm unambiguously the compounds’ structures. The highly efficient CPC separation developed in this work provides valepotriates in amounts suitable for further study and strong bases for future industrial development.