1. Division of Experimental Therapeutics, Walter Reed Army Institute of Research, Silver Spring, Maryland, United States
2. Medicines for Malaria Venture, International Center Cointrin, Route de Pre-Bois 20, P.O. Box 1826, CH-1215 Geneva 15, Switzerland
3. United States Army Medical Component, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
4. Department of Chemistry, University of Pittsburgh, Parkman Avenue, CSC 1301, Pittsburgh, Pennsylvania 15260, United States