1. Department of Chemistry, The University of Sussex, Falmer, Brighton BN1 9QJ, U.K., Pfizer Pharmaceuticals Limited, Sandwich, Kent CT13 9NJ, U.K., and AstraZeneca, Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG, U.K. P.J.Parsons@sussex.ac.uk