1. Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
2. Department of Pharmaceutical Sciences, University of California, Irvine, CA 92697, USA
3. Department of Chemistry, University of California, Irvine, CA 92697, USA
4. Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA