1. Department of Chemistry, School of Arts and Sciences, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218-2685, Division of Clinical Pharmacology, Department of Medicine, School of Medicine, The Johns Hopkins University, Baltimore, Maryland 21205, The Johns Hopkins Malaria Research Institute, Bloomberg School of Public Health, Baltimore, Maryland 21205, and National Cancer Institute Center for Cancer Research, National Institutes of Health, Bethesda, Maryland 20892-5065