1. Chemical Biology Laboratory,
Molecular Discovery Program, Center for Cancer Research, National Cancer Institute-Frederick, Frederick, Maryland
21702, United States
2. Laboratory
of Metabolism, Center
for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, United
States
3. Department of Biology
and Biological
Engineering, Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139,
United States
4. Institute
of Organic Chemistry, University of Leipzig, Leipzig, Germany