Abstract:
The effect of infectious diseases on the population in the developing countries is of utmost concern. Malaria, tuberculosis (TB) and human immunodeficiency virus (HIV) are the three major infectious disease threats. They account for approximately half of the mortality caused by infectious diseases, which is almost half of the mortality in the developing countries. With no vaccine likely in the foreseeable future, drugs remain the best means of controlling infectious diseases. In the industrialized nations at the present time, some 50% of all prescribed drugs are derived or synthesized from natural products (animals, marine species, plants and micro-organisms). It has been estimated that plants are the most important source of medicine for more than 80% of the world’s population. As previous work on the leaves of Croton steenkampianus gave promising results and revealed that it still contained bioactive compounds that could be isolated, it was chosen for further work. The bioassay guided fractionation of the ethanol crude extract using silica and Sephadex column chromatography resulted in the isolation of six compounds: three flavoniods (quercetin, tamarixetin and eriodictyol), one new indane (1) (2,6-dimethyl-1-oxo-4 indanecarboxylic acid) and two new diterpenes (steenkrotin A (2) and steenkrotin B (3)) with novel skeletons. The structure of the compounds was determined using NMR, IR, UV, MS and X-ray crystallography. Ethanol crude extract, quercetin, steenkrotin A, steenkrotin B and the indane were tested against four strains of Plasmodium falciparum (D6, D10, Dd2 and W2). Quercetin showed good antiplasmodial activity against the D10 and Dd2 strains. The antiplasmodial activity of steenkrotin A and crude extract were moderate. The antimalarial activity of steenkrotin A in particular is promising, as it showed more activity against resistant strains. The indane, and steekrotin B were not active against the strains of P. falciparum used (IC50 > 10 μg/m). The IC50 of the compounds improved when they were combined with chloroquine. However, the IC50 of chloroquine was still the lowest. The compounds showed moderate bioactivity against Bacillus cereus and Escherichia coli. The three new compounds (1, 2 and 3) tested against Mycobacterium (H37Rv) were not active (IC50 > 10 μg/ml). The indane (1) showed anti-HIV activity at 50 μg/ml against reverse transcriptase. The antioxidant activity of the compounds tested ranged from weak to excellent (>280.00 μg/ml for compound 1 and 2 to 0.05 μg/ml for quercetin). The cytotoxicity of the compounds and extract were determined against Vero cells lines. Their IC50 values ranged from 34.0 to 305.9 ìg/ml, which is higher and better than that of chloroquine. The IC50 values obtained are: chloroquine (25.0), quercetin (33.6), steenkrotin A (35.0), ethanol extract (45.0), tamarixetin (53.8), indane (248.2) and steenkrotin B (305.9).
