1. Research Center for Marine Drugs, School of Pharmacy, Second Military Medical University, 325 Guo-He Road, Shanghai 200433, People's Republic of China, Department of Chemistry, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany, and Institut für Mikrobiologie, Technische Universität Braunschweig, Spielmannstrasse 7, 31806 Braunschweig, Germany