1. Department of Organic Chemistry, Faculty of Science, 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. Department of Microbiology, Faculty of Science, University of Yaoundé I, Yaoundé, Cameroon