1. Department of Chemistry, the Royal Institute of Technology, S-100 44 Stockholm, Sweden, Medical Products Agency, Box 26, S-751 03 Uppsala, Sweden, Astra Hässle AB, S-431 83 Mölndal, Sweden, and Institute of Chemistry, University of Wroclav, 14 F Juliet-Curie Street, 50-383 Wroclav, Poland