1. Biological Chemistry, Division of Biomedical Sciences, Sir Alexander Fleming Building, Imperial College of Science, Technology and Medicine, London SW7 2AZ, U.K., and Preclinical Safety Evaluation, GlaxoSmithKline Research & Development, Ware, Herts., SG12 0DP, U.K., and Analytical Technologies, GlaxoSmithKline R & D, Stevenage, Herts. SG1 2NY, U.K.