1. Institut für Organische und Analytische Chemie , Universität Bremen , Leobener Strasse 7 (NW2C) , Bremen 28359 , Germany
2. Department of Organic Chemistry, Higher Teachers’ Training College , University of Yaounde I. , P. O. Box 47 , Yaoundé , Cameroon
3. Department of Pharmacognosy , University of Ibadan , Ibadan , Nigeria
4. Department of Pharmaceutical and Medicinal Chemistry, Faculty of Pharmaceutical Sciences , University of Nigeria , Nsukka , 410001 Nigeria
5. National Center for Natural Products Research , School of Pharmacy , University of Mississippi , MS 38677 , USA
6. Chemistry Department , University of Buea , P. O. Box 63 , Buea , Cameroon
7. Department of Pharmaceutical Chemistry , Martin-Luther-Universitat Halle-Wittenberg , Wolfgang-Langenbeck Str. 4 , Halle (Saale) 06120 , Germany
8. Department of Informatics and Chemistry , University of Chemistry and Technology Prague , Technická 5 166 28 , Prague 6 Dejvice , Czech Republic