1. Department of Pharmaceutical Chemistry, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem 91120, Israel, Carlson School of Chemistry, Clark University, 950 Main Street, Worcester, Massachusetts 01610, and Division of Bone & Mineral Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue (HIM 944), Boston, Massachusetts 02215