Anti-plasmodial and cholinesterase inhibiting activities of some constituents of Psorospermum glaberrimum

Glaberianthrone (1), a new bianthrone was isolated from the hexane extract of the stem bark of Psorospermum glaberrimum together with thirteen known compounds: 3-geranyloxyemodin anthrone (2), friedelan-3-one (3), 3-prenyloxyemodin anthrone (4), 3-geranyloxyemodin (5), 3-prenyloxyemodin (6), friedelan-3-ol (7), acetylvismione D (8), betulinic acid (9), 2-geranylemodin (10), bianthrone A2b (11), bianthrone 1a (12), emodin (13) and 2-prenylemodin (14). The structures of the isolated compounds were established by means of spectroscopic methods. The extracts and the isolated compounds were tested in vitro for their anti-plasmodial activity against Plasmodium falciparum (chloroquine resistant strain W2) and for their acetyl- and butyryleholinesterase inhibitory properties. The n-hexane extract showed good anti-plasmodial activity against P falciparum W2 strain, with IC50 of 0.87 mu g/ml. It also exhibited 65.5% and 98.2% of acetyl- and butyrylcholinesterase inhibition at 0.2 mg/ml, respectively. Compounds 2 and 8 showed the best potencies against P falciparum W2 strain with IC50 of 1.68 mu M and 0.12 mu M, (0.66 mu g/ml and 0.054 mu g/ml) respectively. All tested compounds showed good butyrylcholinesterase inhibition activities with compound 12 displaying the best potency (IC50 9.25 +/- 0.25 mu M). All the tested compounds showed weak inhibitory activity against acetylcholinesterase.