1. Division of Natural Drug Discovery, Institute of Natural Medicine, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
2. Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
3. Faculté des Sciences, Université de Kinshasa, B.P. 202, Kinshasa XI, Democratic Republic of the Congo