1. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
2. Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
3. Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
4. Edwin L. Steele Laboratory
for Tumor Biology, Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, 100 Blossom Street, Cox-7, Boston, Massachusetts 02114, United States