1. a Division of Organic Chemistry 2 , University of Lund , P.O.B. 124, S-221 00, Lund, Sweden
2. b Lehrbereich Biotechnologie der Universität Kaiserslautern , Paul Ehrlich-Str. 23, D-67663, Kaiserslautern, F.R.G.
3. c Department of Biochemistry , Research Institute of Biological Psychiatry, ST Hans Hospital , DK-4000, Roskilde, Denmark