1. Organic and Bioorganic Chemistry, Department of Chemistry, Bielefeld University, D-33501 Bielefeld, Germany
2. Chemistry Department, Faculty of Science, Al-Azhar University, Nasr City-Cairo 11884, Egypt
3. Microbial Chemistry Department, Division of Genetic Engineering and Biotechnology Research, National Research Centre, El-Behoos St. 33, Dokki-Cairo 12622, Egypt
4. Centrum für Biotechnologie (CeBiTec), Bielefeld University, Universitätsstraße 27, D-33615 Bielefeld, Germany
5. Chemistry of Natural Compounds Department, Division of Pharmaceutical Industries, National Research Centre, El-Behoos St. 33, Dokki, Cairo 12622, Egypt , Tel.: +202-270-1728/int-2609. Fax: +202-333-70931