In recent years, it has been suggested that the 5-HT5A receptor which is one of the subtypes of serotonin receptors plays an important role in dementia and schizophrenia. For example, it has been reported that new exploratory behaviors are increased in the 5-HT5A receptor knock-out mice, and hyperactivity by LSD is inhibited in the 5-HT5A receptor knock-out mice (Neuron 22, 581-591, 1999). From the results of gene expression analysis, it has been reported that the 5-HT5A receptor is highly expressed in human and rodent brain, and in brain, it is highly expressed in hippocampal CA1 and CA3 pyramidal cells which are related to memory, and frontal lobe (cerebral cortex) which is deeply related to schizophrenia (Molecular Brain Research 56, 1-8, 1998). Furthermore, it has been reported that gene polymorphism of the 5-HT5A receptor relates to schizophrenia (Neuroreport 11, 2017-2020, 2000; Mol. Psychiatr. 6, 217-219, 2001; and J. Psychiatr. Res. 38, 371-376, 2004). Accordingly, it is suggested that regulation of 5-HT5A receptor action leads to the improvement of dementia and schizophrenia and compounds with such function are needed.
Hitherto, several kinds of compounds having affinity for a 5-HT5A receptor have been reported.
For example, it is described that bicyclic acylguanidine derivatives represented by the following general formula bind to the 5-HT5A receptor, and are thus used for treating dementia, schizophrenia, and the like (Patent Document 1).

(A represents phenyl or the like, R1, R2, and R3 each represent H, lower alkyl, halogen, or the like, R7 and R8 each represent H, lower alkyl, or the like, X represents O, S, or CR9aR9b, R9a and R9b each represent H or the like, the dotted line represents a bond or absence, m represents 0, 1, or 2, L1 and L2 each represent a bond or the like, and R4, R5, and R6 each represent H or the like. For details, refer to the publication.)
In the publication, there is no disclosure on those in which the bicyclic ring group has a N atom containing ring.
In addition, it is reported that compounds having a tricyclic acylguanidine structure (Patent Document 2) and compounds having a structure in which the ring is directly bonded to the guanidine (Patent Document 3) each bind to the 5-HT5A receptor, and are used for treating dementia, schizophrenia, and the like.
Furthermore, it is described that quinoline derivatives represented by the following general formula bind to a 5-HT5A receptor, and are used for treating dementia, schizophrenia, and the like (Patent Document 4).

(R1 represents —C(O)NRcCH2—Ar1 or the like, R2 represents —Ar2, —CHRd—Ar2, —CH2CH2O—Ar2, or the like, R3 represents phenyl or pyridinyl, which may be substituted, Ar1 and Ar2 each represent aryl or heteroaryl, which may be substituted, and Rc and Rd each represent a hydrogen atom or C1-7-alkyl. For details on these, refer to the publication.)
In the publication, there is no disclosure on those having acylguanidine as R1.
Hitherto, there is no report for a 5-HT5A receptor modulator which has a structure in which the guanidine is bonded to a bicyclic nitrogen-containing ring via a carbonyl group.
In addition, naphthalene ring derivatives substituted with an acylguanidino group have been reported in Patent Document 5. This document relates to a naphthylacylguanidine derivative, but does not disclose the quinoline derivative of the present invention. Further, the application of the compound of this document is an antiviral agent.