Cholinesterase-Inhibiting Withanolides from Ajuga bracteosa

Three new withanolides, bracteosin A (=(22R)‐5β,6β : 22,26‐diepoxy‐4β,28‐dihydroxy‐3β‐methoxyergost‐24‐ene‐1,26‐dione; 1), bracteosin B (=(22R)‐5β,6β : 22,26‐diepoxy‐4β,28‐dihydroxy‐3β‐methoxy‐1,26‐dioxoergost‐24‐en‐19‐oic acid; 2), and bracteosin C (=(22R)‐22,26‐epoxy‐4β,6β,27‐trihydroxy‐3β‐methoxyergost‐ 24‐ene‐1,26‐dione; 3), have been isolated from the whole plants of Ajuga bracteosa. Their structures were deduced by spectral analysis, including 1D‐ and 2D‐NMR techniques. In addition, dihydroclerodin‐1, clerodinin A, lupulin A, and dihydroajugapitin have also been isolated for the first time from this species. Compounds 1–3 exhibited evident inhibitory potential against cholinesterase enzymes in a concentration‐dependent fashion.