1. Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
2. Department of Medicine, Washington University in St. Louis, St. Louis, Missouri 63130, United States
3. Center for Metabolomics and Isotope Tracing Washington University in St. Louis, St. Louis, Missouri 63130, United States
4. Epidemiology, Biostatistics and Biodemography, Department of Public Health, University of Southern Denmark, Odense 5230, Denmark
5. Siteman Cancer Center, Washington University in St. Louis, St. Louis, Missouri 63130, United States