1. Department of Chemistry, Birkbeck College, University of London, Gordon House, 29 Gordon Square, London WC1H 0PP, U.K., Department of Safety of Medicines, Zeneca Pharmaceuticals, Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG, U.K., Bruker Analytische Messtechnik GmbH, Silberstreifen, D-76287 Rheinstetten, Germany, and Hoechst-Roussel, Walton Manor, Walton, Milton Keynes, Buckinghamshire MK7 7AJ, U.K.