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, R 5 represents optionally substituted aryl or the like, Z represents - N=CHR 6 R 7 or the like, R 6 and R 7 represent H, optionally substituted alkyl, optionally substituted aryl or the like, R 101 and R 102 together form =O, and R 103 and R 104 represent H, or R 101 and R 104 together from a bond, and R 102 and R 103 together form a bond.
