1. Department of Chemistry, The Joseph Black Building, University of Glasgow, Glasgow, G12 8QQ, U.K., The School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, U.K., UCB Celltech R&D Ltd, 216 Bath Road, Slough, Berkshire, SL1 4EN, U.K., and Pfizer Global Research & Development, Sandwich, Kent, CT13 9NJ, U.K.