1. Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu ProvinceLanzhou Institute of Chemical PhysicsChinese Academy of Sciences Lanzhou 730000 P. R. China
2. University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. State Key Laboratory of Applied Organic ChemistryLanzhou University Lanzhou 730000 P. R. China
4. Key Laboratory of Heavy Ion Radiation Biology and Medicine of, Chinese Academy of SciencesInstitute of Modern Physics Lanzhou 730000 P. R. China