Evaluation of insecticidal and anti-hookworm activities of crude extracts and isolates from dichapetalum madagascariense stem bark

Abstract

The constituents of the roots of Dichapetalum madagascariense have been investigated for their anti-tumour and anti-proliferative activities on some cancer cell lines and anti-parasitic activities against some causative pathogens of selected neglected tropical diseases. The most active constituents were the dichapetalins. To investigate the constituents of the stem bark of the plant for potential insecticidal and anti-hookworm activities, chromatographic separation of the stem bark extracts gave four commonly occurring triterpenoids; friedelan-3β-ol (1), friedelan-3-one (2), the relatively rare triterpenoid zeylanol (3), β-sitosterol (4) and stigmasterol (5), which was obtained as a mixture with (4). This is the first report of the presence of zeylanol (3) in D. madagascariense. Activity against the maize weevil, Sitophilus zeamais gave LD₅₀ values (µg/mL) of 0.48 (compound 1), 0.56 (2), 0.52 (mixture of 1 and 2), and 0.98 (mixture of 4 and 5). Crude extract-treated maize grains at doses ≥ 2 g per 100 g grain provided the most effective protection to maize against hidden eggs and immature stages of S. zeamais compared to complete protection at the highest dosage (10 g/100 g grain). The IC₅₀ of tested compounds against human hookworm Necator americanus showed lower potencies (0.64-1.33 µg/µL) than the standard, albendazole (0.0024 µg/µL). This study has established the presence of zeylanol (3) in D. madagascariense and shown that the insecticidal activity of the tested compounds and extracts against S. zeamais could provide some protection against maize grains but at levels that are uneconomical for incorporation into sustainable pest management programmes. Anti-hookworm activities obtained may serve as leads for further optimization and development in the anthelmintic drug discovery efforts.