1. Chemistry and Life Sciences Group, Research Triangle Institute, P.O. Box 12194, Research Triangle Park, North Carolina 27709, LTF-Universidade Federal da Paraiba, Caixa Postal 5009, 58059 Joao Pessoa, PB, Brazil, and Program for Collaborative Research in the Pharmaceutical Sciences and Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, Chicago, Illinois 60612