1. Chemistry Research Laboratory, University of Oxford, Mansfield Road, OX1 3TA, UK
2. Department of Oncology, University of Oxford, Old Road Campus Research Building, Oxford, OX3 7DQ, UK
3. Department of Chemistry, King's College London, 7 Trinity Street, London, SE1 1DB, UK
4. Shandong Laboratory of Yantai Drug Discovery, Bohai Rim Advanced Research Institute for Drug Discovery, Yantai, Shandong 264117, P. R. China