1. Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine; Institute of Radiation Medicine; Chinese Academy of Medical Sciences & Peking Union Medical College; Tianjin 300192 P.R. China
2. Department of Chemistry; Brandeis University; Waltham MA 02454 USA
3. State Key Laboratory of Medicinal Chemical Biology; Nankai University; Tianjin 300071 P.R. China