1. Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
2. Division of Chemical Biology & Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, Texas 78712, United States
3. Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan
4. Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas 78712, United States