Isolation and cholinesterase-inhibition studies of sterols from Haloxylon recurvum

Haloxysterols A–D (1–4), new C-24 alkylated sterols, have been isolated from the chloroform soluble fraction of Haloxylon recurvum, along with five known sterols 5–9, which are reported for the first time from this species. Their structures were determined by means of 1D- and 2D-NMR techniques. Compounds 1–9 inhibited cholinesterase enzymes in a concentration-dependent manner with Ki values ranging between 0.85–25.5 and 1.0–19.0 μM against acetylcholinesterase (AChE; EC 3.1.1.7) and butyrylcholinesterase (BChE; EC 3.1.1.8) enzymes, respectively. Lineweaver–Burk, Dixon plots and their secondary replots indicated that compounds 1–9 are non-competitive inhibitors of both AChE and BChE enzymes.