Compounds from Gum Ammoniacum with Acetylcholinesterase Inhibitory Activity

The use of herbal medicinal preparations in dementia therapy has been studied based on experience from traditional medicine. A dichloromethane extract of gum ammoniacum, the gum-resin from Dorema ammoniacum D. Don had shown acetylcholinesterase (AChE) inhibitory activity in a previous study. The aim of this study was the isolation and characterization of the active compounds from this resin. The extract was investigated by a respective colorimetric microplate assay and the active zones were identified via TLC bioautography and isolated using several chromatographic techniques. The structures of the active components were characterized by one- and two-dimensional ¹H and ¹³C NMR spectroscopy and mass spectrometry as (2'S,5'S)-2'-ethenyl-5'-(3-hy-droxy-6-methyl-4-oxohept-5-en-2-yl)-7-methoxy-2'-methyl-4H-spiro[chromene-3,1'-cyclopentane]-2,4-dione (1), which is an analogue of doremone A and a new natural compound, and as (2'S,5'R)-2'-ethenyl-5'-[(2R,4R)-4-hydroxy-6-methyl-3-oxohept-5-en-2-yl]-7-methoxy-2'-methyl-4H-spiro[chromene-3,1'-cyclo-pentane]-2,4-dione (2 = doremone A), (4E,8E)-1-(2,4-dihydroxyphenyl)-5,9,13-trimethyltetradeca-4,8,12-trien-1-one (3 = dshamirone), and 4,7-dihydroxy-3-[(2E,6E)-3,7,11-trimethyldodeca-2,6,10-trien-1-yl]-2H-chromen-2-one (4 = am-moresinol). Dshamirone turned out to be the most active compound with an IC50 value for AChE inhibitory activity of 23.5 μM, whereas the other substances showed weak activity. The concentrations of the analytes in the resin were determined by HPLC as 3.1%, 4.6%, 1.9%, and 9.9%, respectively.