1. Key Laboratory of Oil & Gas Fine Chemicals, Ministry of Education & Xinjiang Uyghur Autonomous Region, College of Chemistry and Chemical Engineering Xinjiang University Urumqi 830046 People's Republic of China
2. Roy and Diana Vagelos Laboratories, Department of Chemistry University of Pennsylvania 231 South 34th Street Philadelphia, Pennsylvania 19104-6323 USA
3. Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, School of Chemical Science and Technology Yunnan University Kunming 650091 People's Republic of China