A new dammarane triterpenoid and other secondary metabolites from selected three annonaceous plant species

This dissertation reports on the isolation and characterization of three terpenoids including a new dammarane triterpenoid from Isolona heinsenii, sterols from Lettowianthus stellatus as well as a flavonoid and phenyltetralin lignin from Polyceratocarpus schefflerii. The larvicidal activities against Aedes aegypti mosquito larvae of crude extracts and some isolated compounds are also reported. The ethanol extracts of root and stem bark of I. heinsenii yielded two known terpenoids, namely polycarpol (75) and the indole sesquiterpene, polyalthenol (76). Polyalthenol and the new dammarane triterpenoid, heinsenol (81) were also isolated from the ethanol extract of the leaves of I. heinsenii. The ethanol leaves extract of L. stellatus yielded a mixture two steroids β-sitosterol (103) and stigmasterol (104). From the ethanol extracts of the root bark of P. schefflerii a known flavonoid, catechin (105) and the known phenyltetralin lignin, lyoniside (108) were isolated. The structures of the isolated compounds were determined by using NMR and MS data. All crude extracts from P. schefflerii showed poor larvicidal activity. On the other hand, the crude extracts of leaves and root bark from I. heinsenii exhibited good larvicidal activity with LC50 values of 50 µg/mL and 30 µg/mL; and LC50 values 20 µg/mL and 10 µg/mL for 48 hours and 72 hours, respectively. The ethanol stem bark extracts of I. heinsenii showed a moderate activity by having 200 µg/mL and 150 µg/mL for 48 hours and 72 hours, respectively. When evaluated for their larvicidal activity, polycarpol exhibited activity with LC50 value 200 µg/mL after 72hours while polyalthenol exhibited significant activity with LC50 value 20 µg/mL, 5 µg/mL and 3 µg/mL after 24, 48 and 72 hours. The results obtained are clear indication of the potential that still lies in uninvestigated plants species for control of malaria vector.