1. Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
2. Department of Pharmacy, Division of Pharmaceutical Chemistry, University of Athens, Panepistimiopoli-Zografou, Athens 15771, Greece
3. Physiology Group, Biomedical Sciences Division, King's College London, Campden Hill Road, London W8 7AH, U.K.