Cholinesterase and BACE1 inhibitory diterpenoids from Aralia cordata.

Fourteen diterpenes were isolated from the n-hexane fraction of the roots of Aralia cordata (syn. = A. continentalis). Through spectroscopy, the chemical structures were determined as: ent-pimara-8(14),15-diene-19-oic acid (1); ent-kaur-16-en-19-oic-acid (2); 18-nor-ent-pimara-8(14),15-diene-4beta-ol (3); 18-nor-ent-kaur-16-ene-4beta-ol (4); ent-pimara-8(14),15-diene-19-ol (5); 7alpha-hydroxy-ent-pimara-8(14),15-diene-19-oic acid (6); 7beta-hydroxy-ent-pimara-8(14),15-diene-19-oic acid (7); ent-pimar-15-en-8alpha,19-diol (8); 7-oxo-ent-pimara-8(14),15-diene-19-oic acid (9); 16alpha-hydroxy-17-isovaleroyloxy-ent-kauran-19-oic acid (10); 17-hydroxy-ent-kaur-15-en-19-oic acid (11); 15alpha,16alpha-epoxy-17-hydroxy-ent-kauran-19-oic acid (12); 16alpha,17-dihydroxy-ent-kauran-19-oic acid (13); and 16alpha-methoxy-17-hydroxy-ent-kauran-19-oic acid (14). Compounds 4, 5, 8, 12, and 14 were first isolated from this plant. The anti-Alzheimer and antioxidant effects of ent-pimarane-type diterpenes 1, 3, 5, 8, and 9, as well as ent-kaurane-type diterpenes 2, 4, and 10-13, were evaluated via beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), peroxynitrite (ONOO(-)), and nitric oxide (NO*) assays. Of the compounds tested, 8 exerted the most effective BChE inhibition with an IC(50) value of 7.58 microM, followed by 3, 13, 11, 2, and 10. Compounds 9-11 exhibited good BACE1 inhibitory activities with IC(50) values of 18.58-24.10 microM. However, 11 showed marginal AChE inhibitory effect, and all compounds tested showed no scavenging activities on ONOO(-) and NO* at a concentration of 100 microM.