1. Department of Organic Chemistry, Faculty of Science, University of Yaounde I, P.O. Box 812, Yaounde, Cameroon
2. Department of Chemistry, University of Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
3. Department of Chemistry, Higher Teachers’ Training College, University of Yaounde I, BP 47, Yaounde, Cameroon