1. Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, U.K., Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, U.K., and GlaxoSmithKline Medicines Research Centre, Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2NY, U.K.