1. College of Pharmacy, University of Nebraska Medical Center, 986025 Nebraska Medical Center, Omaha, Nebraska 68198-6025, Pharma Division, Preclinical Research, F. Hoffmann-LaRoche Ltd., CH-4070 Basel, Switzerland, Swiss Tropical Institute, CH-4002 Basel, Switzerland, Department of Chemistry, University of Nebraska at Omaha, 60th and Dodge Street, Omaha, Nebraska 68192-0109