1. Department of Organic Chemistry, Faculty of Science, TWAS Research Unit (TRU) of the University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
2. Department of Chemistry, Higher Teacher’s Training College, University of Yaoundé I, P.O. Box 47, Yaoundé, Cameroon
3. Department of Chemistry, Organic and Bioorganic Chemistry, Bielefeld University, P.O. Box 100131, 33501 Bielefeld, Germany