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.

Graphical abstractHaloxysterols A–D (1–4), together with 5 known sterols (5–9), were isolated from the whole plant of Haloxylon recurvum. The structures were elucidated on the basis of spectral methods, especially 2D-NMR spectra (HMQC, HMBC, and NOESY). All the compounds showed potent inhibitory activity against cholinesterase enzyme.Figure optionsDownload full-size imageDownload as PowerPoint slide