1. Departments of Chemistry and Pharmacology, University College London, Gower Street, London WC1E 6BT, U.K., Departamento de Quimica Organica, Facultad de Farmacia, Universidad de Granada, Campus de Cartuja, s/n, 18071 Granada, Spain, and Department of Pharmaceutical Chemistry, School of Pharmacy, Aristotelian University of Thessaloniki, Thessaloniki, 540 06, Greece