1. Natural Products Discovery Group, ‡Institute for Natural
Products Applications and Research Technologies, and §Department of Chemistry and Biochemistry,
Stephenson Life Sciences Research Center, 101 Stephenson Parkway, University of Oklahoma, Norman, Oklahoma 73019-5251, United States
2. Department of Pharmacology, ∥Cancer Therapy & Research Center, and #Department of Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229, United States