1. State Key Laboratory of Applied Organic Chemistry College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
2. State Key Laboratory of Drug Research Shanghai Institute of Materia Medica Chinese Academy of Sciences 555 Zuchongzhi Road Shanghai 201203 P. R. China
3. McGill University AIDS Center Lady Davis Institute for Medical Research Jewish General Hospital Montreal Quebec H3T 1E2 Canada
4. Shandong Laboratory of Yantai Drug Discovery Bohai Rim Advanced Research Institute for Drug Discovery Yantai Shandong 264117 P. R. China