1. Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
2. Cancer Research U.K./MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Old Road Campus Research Building, Oxford OX3 7DQ, U.K.
3. Chemical Biology and Therapeutics, Novartis Institutes for BioMedical Research, Fabrikstrasse 22, 4054 Basel, Switzerland