1. Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Post Office Box 521 H-6701 Szeged, Hungary, Department of Organic Chemistry, Vrije Universiteit Brussel, B-1050 Brussels, Belgium, Department of Inorganic and Analytical Chemistry, University of Szeged, Post Office Box 440, Szeged, Hungary, Institute of Pharmaceutical Chemistry, University of Szeged, Post Office Box 121 H-6701 Szeged, Hungary, and Clinical Research Institute of Montreal, Montreal, Quebec, H2W 1R7 Canada