1. Department of Chemistry, Lash Miller Laboratories, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6, Institute of Pharmaceutical Chemistry, University of Szeged, 6720 Szeged, Eotvos u. 6, Hungary, and Department of Medicinal Chemistry, University of Szeged, Dom ter 8, 6720 Szeged, Hungary