1. Department of Organic Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden, Department of Clinical Sciences, Section of Oncology, Lund University, Barngatan 2:1, SE-221 85 Lund, Sweden, and Department of Experimental Medical Science, Division of Neuroscience, Lund University, Biomedical Center C13, SE-221 84, Lund, Sweden