1. Department of Organic Chemistry, Faculty of Science, University of Yaoundé I, Yaoundé, Cameroon;
2. Department of Chemistry, Faculty of Science and Medicine, University of Fribourg, Fribourg, Switzerland
3. Department of Chemistry, Higher Teacher Training College, University of Yaoundé I, Yaoundé, Cameroon;
4. Department of Biochemistry, Faculty of Science, University of Dschang, Dschang, Cameroon;