1. Department of Medicinal Chemistry School of Pharmacy Qingdao University Qingdao 266021 China
2. Tsinghua-Peking Center for Life Sciences Ministry of Education Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology Center for Synthetic and Systems Biology Department of Chemistry Tsinghua University Beijing 100084 China
3. Bayer AG Department of Medicinal Chemistry Aprather Weg 18A 42096 Wuppertal Germany