Withania somnifera Dunal (Solanaceae), commonly known as ashwagandha, is the most popular botanical used within the Hindu traditional Ayurvedic system of medicine, where it is predominantly utilized for the treatment of arthritis, anxiety, and stress. Beginning in 1965 with the discovery of withaferin A (1), researchers have invested five decades in pursuit of the phytochemical constituents responsible for these activities. Such exhaustive research has resulted in the discovery of 167 natural products, which include a variety of C28 steroids that are commonly known as withanolides (1-127). Our in depth analysis of published NMR values revealed inconsistent data related to ten withanolide structures (58, 59, 83, 85, 86, 87, 93, 101, 103 and 126). Subsequent structural elucidations utilizing these data revealed that withasomnilide (58), 6β,7β-epoxy-5α,14α,17α-trihydroxy-1-oxo-witha-2,24-dienolide (59), 27-acetoxy-5β-chloro-4β,6α-dihydroxy-1-oxo-witha-2,24-dienolide (93), and sominolide (103) are more likely withanone (40), 20-deoxy-14α-hydroxy-withanolide Y (59a), 27-acetoxy-6α-chloro-4β,5β-dihydroxy-1-oxo-witha-2,24-dienolide (93a), and withaferin A (1), respectively. Herein we discuss these discrepancies, and present the first comprehensive review of the species that compiles all phytochemical discoveries made between 1965 and 2014.
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