1. Centre for Drug Research, Faculty of Pharmacy, P.O. Box 56, FI-00014 University of Helsinki, Finland, Institute of Biotechnology, P.O. Box 56, FI-00014 University of Helsinki, Finland, Division of Pharmaceutical Chemistry, Faculty of Pharmacy, P.O. Box 56, FI-00014 University of Helsinki, Finland, Division of Pharmaceutical Biology, Faculty of Pharmacy, P.O. Box 56, FI-00014 University of Helsinki, Finland, and Technical Research Centre of Finland, VTT, P.O. Box 1000, FI-02044 VTT (Espoo), Finland