Metabolic characterization of withania somnifera from different regions of India using NMR spectroscopy

Withania somnifera (L.) Dun. (Solanaceae), known as Indian ginseng, is one of the most popular medicinal plants in India. Considering the importance and common use of this plant, it is necessary to investigate its holistic metabolite profile. However, with existing analytical methods which are based on TLC and HPLC-UV (or MS), it is difficult to obtain information of the whole range of compounds appropriately. In this study, the metabolic characterization of Withania somnifera leaves, stems, and roots collected in six different regions in India was performed using ¹H NMR spectroscopy followed by principal component analysis (PCA) and hierarchical clustering analysis (HCA). Of the parts of Withania somnifera analyzed in this study, the leaf was found to have the widest range of metabolites, including amino acids, flavonoids, lipids, organic acids, phenylpropanoids, and sugars, as well as the main secondary metabolites of the plant, withanolides. The ¹H NMR spectra revealed the presence of two groups of withanolides: 4-OH and 5,6-epoxy withanolides (withaferin A-like steroids) and 5-OH and 6,7-epoxy withanolides (withanolides A-like steroids). The ratio of these two withanolides was found to be a key discriminating feature of Withania somnifera leaf samples from different origins.