1. Departments of Internal Medicine and Medicinal Chemistry, University of Michigan, 1500 East Medical Center Drive, Ann Arbor, Michigan 48109-0934, Laboratory of Structural Matters, Naval Research Laboratory, 4555 Overlook Avenue, Washington, D.C. 20375, and Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas 66160-7417