1. Fachbereich Chemie, Philipps‐Universität Marburg, Hans‐Meerwein‐Straße, 35043 Marburg, Germany, Fax: +49‐6421‐2822189, http://www.uni‐marburg.de/fb15/ag‐meggers
2. Fujian Provincial Key Laboratory of Chemical Biology, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China