1. State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, P.R.C., Graduate School of Chinese Academy of Sciences, Beijing 100049, P.R.C., and Department Chemie, Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, 81377 München, Germany