1. Departments of Chemistry and Chemical Biology, Molecular and Cellular Biology, and Stem Cell and Regenerative Biology, Harvard University, Cambridge, Massachusetts 02138, Chemical Biology Initiative and Program in Cancer Chemical Biology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, and L’Institut de Science et d’Ingénierie Supramoléculaires (ISIS), Université Louis Pasteur, 8 allée Gaspard Monge, 67000 Strasbourg, France