1. Department of Medicinal Chemistry, School of Pharmacy, Institute for Structural Biology and Drug Discovery, Virginia Commonwealth University, Richmond, Virginia 23298-0133, Allos Therapeutics, Inc., 7000 North Broadway, Suite 400, Denver, Colorado 80221, and Physiologie et Physiopathologie Moleculaires, INSERM U 299, Du Globule Rouge, 78 Rue du General Leclerc, 94275 Le Kremlin Bicetre, France