1. Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Division of Hematology/Oncology and Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, Massachusetts 02215, and Department of Molecular Science and Technology, Ajou University, 5 Wonchun-Dong Yeongtong-Gu Suwon, Korea 443-749