1. Biomedical Department, Johnson Matthey Technology Centre, Blount's Court, Sonning Common, Reading, Berkshire RG4 9NH, United Kingdom, Department of Chemistry, UMIST, P.O. Box 88, Manchester M60 1QD, United Kingdom, and CRC Centre for Cancer Therapeutics, The Institute of Cancer Research, 15 Cotswold Road, Belmont, Sutton, Surrey SM2 5NG, United Kingdom