1. ARC Infruitec-Nietvoorbij, Private Bag X5026, Stellenbosch 7599, South Africa
2. Department of Pharmacognosy and National Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, School of Pharmacy, The University of Mississippi, University, Mississippi 38677
3. Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7530, South Africa
4. PROMEC Unit, Medical Research Council, P.O. Box 19070, Tygerberg 7505, South Africa