1. Department of Pharmacology and Toxicology, College of Pharmacy, The University of Arizona, Tucson, Arizona 85721, Bioresources Research Facility, College of Agriculture, The University of Arizona, Tucson, Arizona 85721, Wyeth-Ayerst Research Laboratories, Natural Products Research Section, Pearl River, New York 10965, and Departamento de Ecología, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile