1. University of Padova, Department of Organic Chemistry, Biopolymer Research Center, CNR, Via Marzolo 1, I-35131 Padova, Italy, Bone and Mineral Metabolism Unit, Charles A. Dana Thorndike Laboratories, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02215 USA, and Department of Medicine, University of Pittsburgh, Pennsylvania, USA