1. Department of Animal Biology and Physiology, Faculty of Science, University of Yaounde I, P.O. Box 812, Yaounde, Cameroon
2. Centre for Schistosomiasis and Parasitology, P.O. Box 7244, Yaounde, Cameroon
3. Department of Organic Chemistry, Faculty of Science, University of Yaounde I, P.O. Box 812, Yaounde, Cameroon
4. Department of Chemistry, Higher Teacher Training College, University of Yaounde I, P.O. Box 47, Yaounde, Cameroon
5. Department of Organic and Bioorganic Chemistry, Faculty of Chemistry, Bielefeld University, P.O. BOX 100131, D-33501, Bielefeld, Germany