1. Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, U.K., Eli Lilly & Co. Ltd, Lilly Research Centre, Erl Wood Manor, Windlesham, Surrey GU20 6PH, U.K., and AstraZeneca, Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG, U.K.