Boswellic Acids with Acetylcholinesterase Inhibitory Properties from Frankincense

Abstract

Frankincense, a gum resin secreted from barks of Boswellia species, is reputed in Arabian folk medicine to improve the memory. In this study, the acetylcholinesterase inhibitory effect of extracts of frankincense and their constituents were investigated. The ethyl acetate soluble fraction from methanol extracts showed the greatest inhibition of acetylcholinesterase. Bioassay-guided fractionation was carried out to isolate several boswellic acids, and their structures were determined spectroscopically. The boswellic acids showing the most inhibitory activity on acetylcholinesterase were 11α-hydroxy-β-boswellic acid (1) and 11-keto-β-boswellic acid (5), whilst others isolated i.e. 3α-acetyl-11-keto-β-boswellic acid (2), 3α-acetyl-11α-hydroxy-β-boswellic acid (3), 11α-methoxy-β-boswellic acid (4), β-boswellic acid (6) and α-boswellic acid (7) were inactive. Acetylcholinesterase inhibitory activity appears to be associated with the presence of either the free hydroxyl group or keto group at C-11 and of the free hydroxyl group at C-3 in the ursane skeleton.