1. a Department of Organic Chemistry, Faculty of Science , University of Yaoundé I , PO Box 812, Yaoundé , Cameroon
2. b Department of Bioresource Engineering, Faculty of Agriculture , Yamagata University , Tsuruoka , Yamagata 997-8555 , Japan
3. c Department of Organic Chemistry, Faculty of Science , University of Antananarivo , PO Box 906, Antananarivo 101 , Madagascar