1. Department of Chemistry, Faculty of Science , University of Douala , PO Box 24157 , Douala , Cameroon
2. Hussain Ebrahim Jamal Research Institute of Chemistry, University of Karachi , Karachi 75270 , Pakistan
3. Department of Organic Chemistry, Faculty of Science , University of Yaoundé I , PO Box 812 , Yaoundé , Cameroon
4. Jodrell Laboratory, Natural Capital and Plant Health Department, Royal Botanic Gardens, Kew, Richmond , Surrey TW9 3DS , UK
5. Department of Chemistry , University of Surrey , Guildford, Surrey GU2 7XH , UK