1. Faculty of Science, Department of Organic Chemistry, University of Yaoundé I, Yaoundé, Cameroon
2. Department Chemie, Universität Fribourg, Fribourg, Switzerland
3. Department of Chemistry, Higher Training College, University of Yaoundé I, Yaoundé, Cameroon
4. Faculty of Chemistry, Philipps-Universität Marburg, Marburg, Germany
5. Faculty of Science, Department of Microbiology, University of Yaoundé I, Yaoundé, Cameroon