1. Departamento de Farmacia, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City 04510 DF, Mexico, Department of Internal Medicine, Division of Infectious Diseases, John D. Dingell Veterans Affairs Medical Center and Wayne State University School of Medicine, Detroit, Michigan 48201, and Centre for Pharmacognosy and Phytotherapy, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, U.K.