1. Laboratory of Bio-organic Chemistry, Department of Organic Chemistry, Faculty of Sciences, CP 160/07, University of Brussels, 50 Av. F.D. Roosevelt, B-1050 Brussels, Belgium, Laboratory of Natural Products, Department of Chemistry, Federal University of Sao Carlos, CP 676, 13565−905, Sao Carlos, Brazil, and Institute for Systematics and Population Biology, Zoölogisch Museum, University of Amsterdam, P.O. Box 94766, 1090 GT Amsterdam, The Netherlands