The present invention relates to fluoropiperidine compounds offormula (I), their stereoisomers, isotopic forms or pharmaceuticallyacceptable saltsthereof as 5-HT6 receptor antagonists. In particular the present inventiondiscloses themethods of preparation, pharmaceutical composition, combinations and use offluoropiperidine compounds, their stereoisomers, isotopic forms orpharmaceuticallyacceptable salts thereof. In formula (I), R1 represents phenyl or pyridyl；wherein thephenyl or pyridyl is optionally substituted with one or more groups selectedfromhalogen, (C1-6)-alkyl or halo(C1-6 )-alkyl； R2 represents hydrogen or (C1-6)-alkyl；R3 represents hydrogen or (C1-6)-alkyl； or R2 and R3 can combine together toform(C3-6)- cycloalkyl； R4 represents hydrogen, (C1-6)-alkyl or halo(C1-6)-alkyl；R5represents hydrogen, (C1-6)-alkyl, halo(C1-6)-alkyl or -(CH2)0-3- (C3-6)-cycloalkyl. Thecompounds can be used in the treatment of cognitive disorder mediated by the5-Hydroxytryptamine 6 receptor, wherein said cognitive disorder is selectedfrom thegroup consisting of dementia in Alzheimer's disease, dementia in Parkinson'sdisease,dementia in Huntington's disease, dementia associated with Down syndrome,dementia associated with Tourette's syndrome, dementia associated with postmenopause,frontotemporal dementia, Lewy body dementia, Vascular dementia, dementia inHIV,dementia in Creutzfeldt-Jakob disease, substance-induced persisting dementia,dementia in Pick's disease, dementia in schizophrenia, dementia in generalmedicalconditions and senile dementia.
