1. Department of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, U.K., Avecia, P.O. Box 42, Hexagon House, Blackley, Manchester, M98ZS, U.K., Syngenta, Jealott's Hill Research Station, Bracknell, Berkshire RG42 6ET, U.K., and AstraZeneca Pharmaceuticals, Alderley Park, Macclesfield, Cheshire, SK104TG, U.K.