Large-scale separation of acetylcholinesterase inhibitors from Zanthoxylum nitidum by pH-zone-refining counter-current chromatography target-guided by ultrafiltration high-performance liquid chromatography with ultraviolet and mass spectrometry screening.

A new strategy by converging ultrafiltration high-performance liquid chromatography with ultraviolet and mass spectrometry and pH-zone-refining counter-current chromatography was developed for the rapid screening and separation of potential acetylcholinesterase inhibitors from the crude alkaloidals extract of Zanthoxylum nitidum. An optimized two-phase solvent system composed of chloroform/methanol/water (4:3:3, v/v) was used in this study. And, in the optimal solvent system, 45 mM hydrochloric acid was added to the aqueous stationary phase as the retainer, while 5 mM triethylamine was added to the organic mobile phase as the eluter. As a result, with the purity of over 95%, five alkaloids including jatrorrhizine (1, 340 mg), columbamine (2, 112 mg), skimmianine (3, 154 mg), palmatine (4, 226 mg), and epiberberine (5, 132 mg) were successfully purified in one step from 3.0 g crude alkaloidals extract. And their structures were identified by ultraviolet, mass spectrometry, 1 H and 13 C NMR spectroscopy. Notably, compounds 2, 4 and 5 were firstly reported in Z. nitidum. In addition, acetylcholinesterase inhibitory activities of compounds 1-5 were evaluated, and compounds 3, 4 and 5 exhibited stronger acetylcholinesterase inhibitory activity (IC50 values at 8.52 ± 0.64, 14.82 ± 1.21 and 3.12 ± 0.32 μg/mL, respectively) than berberine (IC50 value at 32.86 ± 2.14 μg/mL, positive control). The results indicated that the proposed method is an efficient technique to rapidly screen acetylcholinesterase inhibitors from complex samples, and could be served as a large-scale preparative technique for separating ionizable active compounds.