1. Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark, Department of Experimental Therapeutics, Johns Hopkins Oncology Center, Bunting-Blaustein Cancer Research Building, 1650 Orleans Street, Baltimore, Maryland 21231, USA, and Chemistry Department, The Royal Veterinary and Agricultural University, 17 Bülowsvej, DK-1870 Frederiksberg, Denmark