1. Department of Pharmaceutical Chemistry, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria, Departamento de Química Orgánica y Biología, Facultad de Ciencias, UNED, Senda del Rey 9, E-28040 Madrid, Spain, and Department of Mineralogy and Crystallography, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria