NMR studies found that a commercially supplied standard reference purported to be Withanolide D was instead Withanolide A - Penman, K; Bone, KM; Hayes, P; De Voss, J; Agarwal, A; Murali, B; Mundkinajeddu, D; Mayachari, A; Shenoy, R; Lehmann, RP (Planta Medica, 2007)