1. Department of Chemistry, School of Natural and Applied Sciences, Masinde Muliro University of Science and Technology, Kakamega, Kenya
2. Department of Chemistry, College of Natural and Applied Sciences, University of Dar es Salaam, Dar es Salaam, Tanzania
3. Department of Chemistry, School of Physical Sciences, University of Nairobi, Nairobi, Kenya
4. National Centre for Natural Products Research, Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi, University, MS, USA
5. Natural Products Utilization Research Unit, Agricultural Research Service, U.S. Department of Agriculture, University, MS, USA