1. Department of Chemistry, Chemistry Laboratory, Faculty of Science, University of Douala, P. O. Box 24157, Douala, Cameroon
2. Royal Botanic Gardens Kew, TW9 3AE, Richmond, Surrey, UK
3. Department of Chemistry, Organic and Bioorganic Chemistry, Bielefeld University, D-33501 Bielefeld, Germany
4. Department of Chemistry, Higher Teacher Training College, University of Yaoundé I, P. O. Box 47, Yaoundé, Cameroon