1. Department of Chemistry, School of Pure and Applied Sciences, Kenyatta University, P.O. Box 43844, Nairobi 00100, Kenya, Center for Traditional Medicine and Drug Research, Kenya Medical Research Institute, P.O. Box 54840, Nairobi 00200, Kenya, and East Africa Herbarium, National Museums of Kenya, P.O. Box 40658, Nairobi 00100, Kenya