Inhibition of acetylcholinesterase enzyme (AChE) was evaluated by TLC in accordance with the methodology described by Elmann, which was later adapted by Rhee et al. (2001). This bioassay consists in the application of the sample to TLC plates and spraying the plate with Ellman’s reagent, which was prepared by mixing
5,5-dithiobis-2-nitrobenzoic acid (DTNB) and a buffer solution of acetylthiocholine iodide (ATCI). The TLC plate was subsequently sprayed with AChE enzyme (3U/mL). After 3 min, enzyme inhibition was observed by the presence of white spots on the yellow plate. The TLC enzyme test is basically qualitative but is still significantly
sensitive. The following solutions were prepared for this test: (1) 50 mM Tris–HCl pH 8 (buffer); (2) 50 mM Tris–HCl pH 8 containing 0.1 M NaCl and 0.02 M MgCl2·6H2O; (3) 1 mM Ellman’s reagent; and (4) 1 mM ACTI. The lyophilized enzyme AChE was diluted in buffer solution (1) to prepare a 1000U/mL enzyme solution. 5 L aliquots
of compounds 1–7 (4 mg/mL) were initially applied to TLC plates (DC-Alufolien, silica gel 60 F254, 0.2 mm Merck). The plate was then sprayed with solutions (3) and (4). After 3 min, which is the time necessary for the solution to completely dry, the plate was sprayed with AChE (3U/mL). After approximately 10 min, the appearance of
white spots was observed and their diameters were immediately measured. Physostigmine was used as positive control.