1. National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, MS 38677, USA
2. Department of Chemistry, University of Nairobi, P.O. Box 30197-00100, Nairobi, Kenya
3. Departments of Pharmacognosy and School of Pharmacy, University of Mississippi, University, MS 38677, USA
4. Departments of Pharmacology, School of Pharmacy, University of Mississippi, University, MS 38677, USA