1. State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, Yunnan, People's Republic of China, Graduate School of Chinese Academy of Sciences, Beijing 100039, People's Republic of China, and German Cancer Research Centre, Pharmaceutical Biology (C015), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany