Characterization of Acetylcholinesterase Inhibitory Constituents from Annona glabra Assisted by HPLC Microfractionation.

The active fraction of the EtOH extract of the stem of Annona glabra against acetylcholinesterase (AChE) was analyzed by combining HPLC microfractionation with a bioassay. The analytical-scale sample was fractionated by HPLC-DAD into 96-well microplates, which, after evaporation, were assayed against AChE. The active subfractions were scaled up by separation over semipreparative HPLC to give 20 compounds. Four of these, (7S,14S)-(-)-N-methyl-10-O-demethylxylopinine salt (3), S-(-)-7,8-didehydro-10-O-demethylxylopininium salt (10), S-(-)-7,8-didehydrocorydalminium salt (11), and 5-O-methylmarcanine D (17), were assigned as new natural products. In addition, compounds 10 and 11 represent the first natural occurrence of 7,8-didehydroprotoberberines. Compound 3, pseudocolumbamine (12), palmatine (15), and pseudopalmatine (16) showed anti-AChE IC50 values of 8.4, 5.0, 0.4, and 1.8 μM, respectively.