1H NMR-based metabolomic analysis coupled with reversed-phase solid-phase extraction for sample preparation of Saposhnikovia roots and related crude drugs

¹H NMR-based metabolomics has been applied in research on food, herbal medicine, and natural products. Although excellent results were reported, samples were directly extracted with a deuterated solvent (e.g., methanol-d₄ or D₂O) in most reports. As primary metabolites account for most of the results, data for secondary metabolites are partially reflected. Consequently, secondary metabolites tend to be excluded from factor loading analysis, serving as a significant unfavorable feature of ¹H NMR-based metabolomics when investigating biologically active or functional components in natural products and health foods. Reversed-phase solid-phase extraction column (RP-SPEC) was applied for sample preparation in ¹H NMR-based metabolomics to overcome this feature. The methanol extract from Saposhnikoviae radix (SR), an important crude drug, was fractionated with RP-SPEC into 5% methanol-eluting fractions, and the remaining fraction was collected. Each fraction was subjected to ¹H NMR-based metabolomics and compared to results from conventional ¹H NMR-based metabolomics. Based on principal component analysis (PCA) and partial least squares projections to latent structures discriminant analysis (PLS-DA), the 5% methanol fraction and conventional method reflected the amount of saccharides such as sucrose on the PC1/PLS1 axes, and wild and cultivated samples were discriminated along those axes. The remaining fraction clearly distinguished SR from Peucedanum ledebourielloides root. The compounds responsible for this discrimination were deemed falcarindiol derivatives and other unidentified secondary metabolites from the s-plot on PLS-DA. The secondary metabolites from original plants were, therefore, presumed to be concentrated in the remaining fraction by RP-SPEC treatment and strongly reflected the species differences. The developed series is considered effective to perform quality evaluation of crude drugs and natural products.