1. National Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, Department of Pharmacognosy, Department of Pharmaceutics, School of Pharmacy, University of Mississippi, University, Mississippi 38677, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh 11451, Saudi Arabia, and Department of Chemistry, Paul M. Gross Chemical Laboratory, Duke University, Durham, North Carolina 27708-0346