1. Contribution from Research and Development, Boehringer Ingelheim (Canada) Ltd., 2100 Cunard Street, Laval, Québec, H7S 2G5, Canada, and Biomolecular NMR Laboratory, Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montréal, Québec, H4P 2R2, Canada