Abstract
Plants have been used as medicinal agents for over a thousand years and have proved to be an important source of many clinical drugs. Several species belonging to the Croton genus (Euphorbiaceace) are employed as traditional medicinal agents in Africa, Asia and South America. The Croton species are popularly used to treat cancer, hypertension, inflammation, rheumatism, bleeding gums, malaria, asthma, syphilitic ulcers, diabetes, pain and ulcers. The Croton genus is rich in alkaloids, flavonoids, triterpenoids, diterpenoids and sesquiterpenoids. Some of the substances that have been isolated from the Croton genus have been evaluated for their biological activities including anti-cancer, anti-hypertensive, anti-inflammatory, anti-malarial, anti-ulcer, anti-viral and anti-microbial effects. The study involved a phytochemical and pharmacological analysis of three Southern African Croton species, C. gratissimus Burchell, C. sylvaticus Hoechst and C. pseudopulchellus Pax which are traditionally used for the treatment of various ailments. Twenty-five diterpenoids, four sesquiterpenoids, six triterpenoids, three phytosterols and two lignan derivatives were isolated from the three plants. The structures of these compounds were determined using FTIR, MS, 1D and 2D NMR studies. Thirteen diterpenoids are reported for the first time, including one cembranoid diterpenoid that possess a new rearranged skeleton. Several of the isolated compounds were screened for cytotoxicity effects against PEO1 and PEO1TaxR (paclitaxel resistant) ovarian cancer cell lines, liver tumour (HUH7 strain) cell line and anti-plasmodial activities against the Plasmodium falciparum (CQS) D10 strain. Compounds CG.3, CG.4, CG.7 and CG.9 displayed moderate cytotoxic effects against the PEOl and PEOlTaxR cell lines. The phytochemical analysis of the three Croton species was also undertaken in order to ascertain the presence of limonoids in the Euphorbiaceae family. This is because limonoids which were thought to be restricted to the Meliaceae, Simaroubaceae and Rutaceae families were reported from the African Croton jatrophoides (Euphorbiaceae). Therefore, the absence of limonoids from the three Croton plants evaluated in this study further raises doubts about the occurrence of limonoids from the Euphorbiaceae family, and about the certainty of identification of the C. jatrophoides Pax that was reported to yield limonoids.