1. Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, U.K., Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, U.K., The Chemistry Laboratory, University of Sussex, Falmer, Brighton, East Sussex, BN1 9QJ, U.K., and GlaxoSmithKline Medicines Research Centre, Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2NY, U.K.