The invention relates to serotonin 5-HT6 receptor antagonists - novel 2-amino-3-arylsulfonyl-6,7,8,9-tetrahydropyrazolo[1,5-a]pyrido[4,3-e]pyrimidines and substituted 2-amino-3-arylsulfonyl-5,6,7,8-tetrahydropyrazolo[1,5-a]pyrido[4,3-d]pyrimidines, drug substances and pharmaceutical compositions comprising the said drug substances as the said compounds, and also to method of prophylaxis and treatment of various diseases of central nervious system in humans and animals pathogenesis of which is associated with serotonin 5-HT6 receptors including cognitive and neurodegenerative diseases.Substituted 2-amino-3-arylsulfonyl-6,7,8,9-tetrahydropyrazolo[1,5-a]pyrido[4,3-e]pyrimidines of the general formula 1 and substituted 2-amino-3-arylsulfonyl-5,6,7,8-tetrahydropyrazolo[1,5-a]pyrido[4,3-d]pyrimidines of the general formula 2 and pharmaceutically acceptable salts and/or hydrates thereof.wherein: Ar represents optionally substituted aryl or optionally substituted heteroaryl R1 represents hydrogen, optionally substituted C1-C3alkyl, C1-C4alkyloxycarbonyl R2 represents hydrogen, halogen or optionally substituted C1-C3alkyl R13 and R23 represent optionally alike: hydrogen, optionally substituted C1-C3alkyl or R13 and R23 together with the nitrogen atom to which they are attached form an optionally substituted azaheterocycle.
