An objective of the present invention is to provide compounds that can effectively suppress the concentration of phosphorus in serum to effectively prevent or treat diseases induced by an increase in concentration of phosphate in serum. The compounds according to the present invention are compounds represented by formula (I) and pharmaceutically acceptable salts and solvates thereof:wherein A represents an optionally substituted five- to nine-membered unsaturated carbocyclic moiety or a five- to nine-membered unsaturated heterocyclic moiety, and represents a single bond or a double bond, R5 represents optionally substituted aryl or the like, Z represents —N═CHR6R7 or the like, R6 and R7 represent H, optionally substituted alkyl, optionally substituted aryl or the like, R101 and R102 together form ═O, and R103 and R104 represent H, or R101 and R104 together from a bond, and R102 and R103 together form a bond.
