Ergostane-type steroids from Euphorbia thymifolia with acetylcholinesterase inhibitory effects

Thymifolisteroid A (1), a previously undescribed ergostane-type steroid, and five known related compounds (2–6), were obtained from Euphorbia thymifolia. The known compounds were identified as 3β-hydroxy-4α,14α-dimethyl-5α-ergosta-8,24(28)-dien-7-one (2), β-sitosterol (3), β-sitosteryl-3-O-glucopyranoside (4), 5α-stigmastane-3,6-dione (5) and (6β)-6-hydroxyergost-4-en-3-one (6). Their chemical structures and absolute configuration were determined through comprehensive spectroscopic and mass spectrometric (MS) analyses. Biological evaluation revealed that compound 3 possessed moderate acetylcholinesterase (AChE) inhibitory activity, with an IC50 value of 14.43 ± 0.68 μM, compared with 4.19 ± 0.25 μM for the positive control drug donepezil. Furthermore, molecular docking and molecular dynamics simulations jointly suggested that compound 3 can stably bind to the active site of AChE.