1. Contribution from the Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, Department of Biochemistry and Division of Cancer Biology and Department of Radiation Oncology, Emory University School of Medicine, Atlanta, Georgia 30322, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Dipartimento Farmaco-Chimico, Università degli Studi di Bari, 70125, Bari, Italy