1. Chemistry and Life Sciences Group, Research Triangle Institute, P.O. Box 12194, Research Triangle Park, North Carolina 27709, Royal Forest Herbarium, Bangkok 10900, Thailand, Department of Chemistry, Mahidol University, Bangkok 10400, Thailand, and Program for Collaborative Research in the Pharmaceutical Sciences, Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, Chicago, Illinois 60612