- 57 - ABSTRACTTo provide a novel vitamin D3 derivative useful as a therapeutic agent for osteoporosis.5 Provided is a vitamin D3 derivative represented bythe following formula (1) or a medicinally acceptable solvate thereof:10 wherein R1 represents a hydrogen atom, an alkyl grouphaving 1 to 6 carbon atoms, an alkylcarbonyloxyalkyl group with each alkyl having 1 to 6 carbon atoms, or an arylcarbonyloxyalkyl group with the aryl having 6 to 10 carbon atoms and the alkyl having 1 to 6 carbon atoms； R215 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms or, together with the other R2 and the carbon atom to which they are bound to, may form a cyclic alkyl group having 3 to 6 carbon atoms； R3 represents an alkyl group having 1 to 6 carbon atoms or, together with20 the other R3 and the carbon atom to which they are bound to, may form a cyclic alkyl group having 3 to 6 carbon atoms； X represents an oxygen atom or a methylene group； and n represents an integer of 1 or 2.
