1. Department of Chemistry, University of Texas at Dallas, P.O. Box 830660, Richardson, Texas 75080, Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, and Macrocyclics, 2110 Research Row, Suite 425, Dallas, Texas 75235