Cholinesterase Inhibiting Withanolides from Withania somnifera

A total of two new (1, 2) and four known (3—6) withanolides were isolated from the whole plant of Withania somnifera. Their structures were elucidated on the basis of spectroscopic techniques and were characterized as 6α,7α-epoxy-3β,5α,20β-trihydroxy-1-oxowitha-24-enolide (1), 5β,6β-epoxy-4β,17α,27-trihydroxy-1-oxowitha-2,24-dienolide (2), withaferin-A (3), 2,3-dihydrowithaferin-A (4), 6α,7α-epoxy-5α,20β-dihydroxy-1-oxowitha-2,24-dienolide (5), and 5β,6β-epoxy-4β-hydroxy-1-oxowitha-2,14,24-trienolide (6), respectively. Compounds 2, 3, 5, and 6 displayed inhibitory potential against butyrylcholinesterase, but only compounds 3, 4, and 6 were found to be active against acetylcholinesterase.