1. Department of Pharmacology, University of Colorado Health Sciences Center, Aurora, Colorado 80045, Echelon Biosciences Inc., Salt Lake City, Utah 84108, Institute for Cancer Studies, School of Medicine, University of Birmingham, Birmingham B15 2TT, United Kingdom, Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84108, and Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80210