1. Laboratory of Pharmacognosy and Phytochemistry, School of Pharmaceutical Sciences, University of Geneva, CH-1211 Geneva 4, Switzerland, Laboratory of Crystallography, Institute of Chemistry, University of Neuchâtel, CH-2009 Neuchâtel, Switzerland, Laboratory of Supramolecular Chemistry of Lanthanides, University of Lausanne, CH-1015 Lausanne, Switzerland, and Department of Tropical Medicine, National Institute of Public Health, BP 1746, Bamako, Mali