Francis O. Shode

Chemical composition and antibacterial activity of the essential oils of Callistemon citrinus and Callistemon viminalis from South Africa.

The chemical composition and the antibacterial activity of the essential oils obtained by hydrodistillation from the leaves of Callistemon citrinus and Callistemon viminalis were analyzed by GC and GC/MS. Twenty-four and twelve components were identified for C. citrinus and C. viminalis, representing 92.0% and 98.3% of the total oils. The major components of C. citrinus and C. viminalis were 1,8-cineole (61.2% and 83.2%) and α-pinene (13.4% and 6.4%), respectively. The in vitro antibacterial activity of the essential oils was studied against 12 bacteria strains using disc diffusion and broth microdilution methods. The oils exhibited strong zone of inhibitions against some bacteria such as S. faecalis (20.3-24.0 mm), both strains of S. aureus (23.0-26.3 mm), B. cereus (17.3-19.0 mm) and S. macrcesens (11.3-23.7 mm) when compared to standard antibiotics gentamycin and tetracycline used as controls. Expect for P. aeruginosa and S. macrcescens, the MIC values of both essential oils ranged from 0.31-2.50 mg/mL.

Anti-Plasmodial Activity of Some Zulu Medicinal Plants and of Some Triterpenes Isolated from Them

Mimusops caffra E. Mey. ex A.DC and Mimusops obtusifolia Lam (both members of the Sapotaceae family), and Hypoxis colchicifolia Bak (family Hypoxidaceae) are used by traditional healers in Zululand to manage malaria. Anti-plasmodial investigation of the crude extracts and some triterpenes isolated from the plants showed activity against a chloroquine sensitive (CQS) strain of Plasmodium falciparum (D10). Among the crude extracts the leaves of M. caffra exhibited the highest activity, with an IC50 of 2.14 μg/mL. The pentacyclic tritepenoid ursolic acid (1), isolated from the leaves of M. caffra was the most active compound (IC50 6.8 μg/mL) as compared to taraxerol (2) and sawamilletin (3) isolated from the stem bark of M. obtusifolia (IC50 > 100). Chemical modification of the ursolic acid (1) to 3β-acetylursolic acid (4) greatly enhanced its anti-plasmodial activity. Compound 4 reduced parasitaemia against Plasmodium berghei by 94.01% in in vivo studies in mice. The cytotoxicity of 3β-acetylursolic acid (IC50) to two human cell lines (HEK293 and HepG2) was 366.00 μg/mL and 566.09 μg/mL, respectively. The results validate the use of these plants in folk medicine.

Antimycobacterial, docking and molecular dynamic studies of pentacyclic triterpenes from Buddleja saligna leaves

Buddleja saligna (family Buddlejaceae) is a medicinal plant endemic to South Africa. Two isomeric pentacyclic triterpenes, oleanolic acid and ursolic acid, were isolated from the leaves of B. saligna using silica gel column chromatography. Compounds oleanolic acid and ursolic acid were subjected to derivatization with acetic anhydride in the presence of pyridine to obtain oleanolic acid-3-acetate and ursolic acid-3-acetate, respectively. The structures of these compounds were fully characterized by detailed nuclear magnetic resonance (NMR) investigations, which included 1H and 13C NMR. Molecular docking studies predicted the free binding energy of the four triterpenes inside the steroid binding pocket of Mycobacterium tuberculosis fadA5 thiolase compared to a reported inhibitor. Thus, their ability to inhibit the growth of M. tuberculosis was predicted and was confirmed to possess significant antimycobacterial activity when tested against Mycobacterium smegmatis, M. tuberculosis H37Rv (ATCC 25177), clinical isolates of multi-drug-resistant M. tuberculosis (MDR-TB) and extensively drug-resistant M. tuberculosis (XDR-TB) using the Micro Alamar Blue Assay. Ursolic acid was isolated from this plant for the first time.

Gunnera perpensa L. : a multi-use ethnomedicinal plant species in South Africa

Gunnera perpensa L. is a medicinal plant used in many parts of South Africa to treat several human ailments. G. perpensa is inherited from and linked to the Siswati, Changana, Sotho, Venda, Shona, Tsonga, and Zulu traditional healing systems, particularly in South African provinces where the plant species is still found in the wild. G. perpensa is declining considerably throughout its natural habitat due to over-exploitation of the plant for its medicinal uses. This review aims to gather the fragmented information on the past and present ethnomedicinal uses, phytochemistry and pharmacological properties of G. perpensa.