1. Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, Department of Biological Chemistry, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois 60064, Department of Hematology and Infectious Diseases, Kumamoto University School of Medicine, Kumamoto 860-8556, Japan, and Experimental Retrovirology Section, HIV and AIDS Malignancy Branch, National Cancer Institute, Bethesda, Maryland 20892