Compounds expressed by the following formula (1) or pharmaceutically permissible solvate thereof which is effective for treating Paget's disease of bone, hypercalcemia or osteoporosis. ##STR00001## In the formula, R.sup.1 is a C.sub.2-C.sub.10 alkyl group, or a C.sub.7-C.sub.15 aralkyl group whose aromatic ring is optionally substituted with a C.sub.1-C.sub.6 alkyl group, a C.sub.1-C.sub.6 alkoxyl group, a hydroxyl group, a halogen atom or a trifluoromethyl group; and R.sup.2 is a C.sub.1-C.sub.10 alkyl group, or a C.sub.7-C.sub.15 aralkyl group whose aromatic ring is optionally substituted with a C.sub.1-C.sub.6 alkyl group, a C.sub.1-C.sub.6 alkoxyl group, a hydroxyl group, a halogen atom or a trifluoromethyl group.