1. Department of Chemistry, University College London; Christopher Ingold Laboratories; 20 Gordon Street London WC1H 0AJ U.K.
2. School of Chemistry; University of Birmingham; Edgbaston, Birmingham B15 2TT U.K.
3. GlaxoSmithKline; Medicines Research Centre; Gunnels Wood Road Stevenage, Herts SG1 2NY U.K.