1. Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K.
2. Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, U.K.
3. Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, U.K.
4. MRC Centre for Drug Safety Science, Department of Pharmacology, School of Biomedical Sciences, University of Liverpool, Liverpool L69 3GE, U.K.