What the devil is in your phytomedicine? Exploring species substitution in Harpagophytum through chemometric modeling of 1H-NMR and UHPLC-MS datasets.

Harpagophytum procumbens (Pedaliaceae) and its close taxonomical ally Harpagophytum zeyheri, indigenous to southern Africa, are being harvested for exportation to Europe where phytomedicines are developed to treat inflammation-related disorders. The phytochemical variation within and between natural populations of H. procumbens (n=241) and H. zeyheri (n=107) was explored using proton nuclear magnetic resonance ((1)H-NMR) and ultra-high performance liquid chromatography coupled to mass spectrometry (UHPLC-MS) in combination with multivariate data analysis methods. The UHPLC-MS results revealed significant variation in the harpagoside content: H. procumbens (0.17-4.37%); H. zeyheri (0.00-3.07%). Only 41% of the H. procumbens samples and 17% of the H. zeyheri samples met the pharmacopoeial specification of ⩾1.2%. Both principal component analysis (PCA) and orthogonal projections to latent structures discriminant analysis (OPLS-DA) indicated separation based on species (UHPLC-MS data OPLS-DA model statistics: R(2)X=0.258, R(2)Y (cum)=0.957 and Q(2)(cum)=0.934; (1)H-NMR data OPLS-DA model statistics: R(2)X=0.830, R(2)Y=0.865 (cum) and Q(2)(cum)=0.829). It was concluded that two species are not chemically equivalent and should not be used interchangeably.