Targeted purification of natural products by orthogonal K-based countercurrent separations

Countercurrent separation (CS) is based on the differences in partition coefficients (K) of analytes distributed between a liquid stationary phase and a liquid mobile phase. The K value is not only an important theoretical parameter in CS, but also has much practical value. K values can be used to predict the CS profiles of analytes, assist in the selection and optimization of CS solvent systems (SSs), guide targeted separations, and enhance the reproducibility of purifications. In the present study we developed a quantitative ¹H NMR (qHNMR)-based approach for simultaneous measurement of K values of multiple components directly from crude plant extracts. Furthermore, two-dimensional selectivity provided by a pair of orthogonal CS SSs was introduced in order to enhance the resolution of difficult-to-separate natural product congeners. Using the K values in optimized orthogonal SSs, a “K map” was created that guided the locating of the target compounds in a series of CS fractions (see figure). These methods were successfully employed in the targeted separation of marker compounds from Ginkgo biloba- and Camellia sinensis-based botanical dietary supplements.