1. Department of Chemistry; University of Dschang; P.O. Box 67 Dschang Cameroon
2. State Key Laboratory of Phytochemistry and Plant Resources in West China; Kunming Institute of Botany, Chinese Academy of Sciences; Kunming 650201 Yunnan P.R. China
3. Institute of Environmental Research (INFU) of the Faculty of Chemistry and Chemical Biology; TU Dortmund; Otto-Hahn-Str. 6 D-44221 Dortmund Germany