The object of the present invention is to provide a low-molecular compound (IL-17 activity inhibitor) having an IL-17 activity inhibitory ability that is more excellent than before. The IL-17RA inhibitor of the present invention contains a compound, or a pharmaceutically acceptable salt, solvate or prodrug thereof, which has an IL-17RA effect that inhibits the binding of interleukin-17A (IL-17A) to humans and the like And, for example, it can be contained in the extracellular domain of human interleukin 17 receptor A (IL-17RA) by Phe60, Gln87, Asp121, Pro122, Asp123, Gln124, Asp153, Cys154, Glu155, Lys160, Pro164, Cys165 , Ser167, Ser168, Gly169, Ser170, Leu171, Trp172, Asp173, Pro174, Pro254, Phe256, Ser258, Cys259, Asp262, Cys263, Leu264, and His266 are bound to IL- through non-covalent bond interactions 17RA, the aforementioned non-covalent bonding interactions include van der Waals, which acts on at least 13 of the amino acid residues, and further preferably contains a predetermined one acting on the amino acid residues At least one type of intermolecular interaction is selected from the group consisting of an ionic bond, a hydrogen bond, a CH-π interaction, and a hydrophobic interaction.本發明之課題在於提供一種具有較已往更為優異之IL-17活性抑制能力的低分子化合物(IL-17活性抑制劑)。本發明之IL-17RA抑制劑含有一化合物、或其製藥上容許之鹽、溶劑合物或前藥，該化合物具有抑制介白素-17A(IL-17A)結合至人類等之IL-17RA作用，並且，例如，可在人類介白素17受體A(IL-17RA)細胞外結構域所含有由Phe60、Gln87、Asp121、Pro122、Asp123、Gln124、Asp153、Cys154、Glu155、Lys160、Pro164、Cys165、Ser167、Ser168、Gly169、Ser170、Leu171、Trp172、Asp173、Pro174、Pro254、Phe256、Ser258、Cys259、Asp262、Cys263、Leu264及His266包圍的空間中，透過非共價鍵性相互作用而結合到IL-17RA，前述非共價鍵性相互作用包含凡得瓦力，其作用在該等胺基酸殘基中之至少13個之間，且進一步宜含有作用在該等胺基酸殘基中預定者之間的選自於由離子鍵、氫鍵、CH-π相互作用及疏水性相互作用所構成群組之至少1種分子間相互作用。
