1. Institut für Chemie, University of Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam-Golm, Germany
2. Department of Biochemistry, Faculty of Science, University of Dschang, Dschang, Cameroon
3. Department of Chemistry, Faculty of Science, University of Dschang, Dschang, Cameroon
4. Department of Pharmaceutical Biology, Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg University, Staudinger Weg 5, 55128 Mainz, Germany