1. Roy and Diana Vagelos Laboratories, Penn/Merck Laboratory for High-Throughput Experimentation, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, United States
2. Department of Process Chemistry, Merck Research Laboratories, P.O. Box 2000, Rahway, New Jersey 07065, United States
3. Institute of Biochemistry & Molecular Biology, School of Life Sciences, Lanzhou University, Southern Tianshui Road 222, Lanzhou 730000, China