1. Department of Medicinal Chemistry and Natural Products, School of Pharmacy-Faculty of Medicine, The Hebrew University, Jerusalem 91120, Israel; Department of Neurosurgery, Johns Hopkins Medical Institution, Baltimore, Maryland 21205; Laboratoire de Chimie Bio-Organique, UMR 6001 CNRS, Faculté des Science, Université de Nice Sophia-Antipolis, 06108 Nice Cédex 2, France; and Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem 91905, Israel