A compound, which is a piperidine derivative of formula (I) or a pharmaceutically acceptable salt or hydrate thereof: ** Formula ** wherein R1 is selected from H, cyano, ureido, alkenyl； acrylic acid or an alkyl or hydroxyalkylamide ester thereof； aminoalkyl optionally substituted with an alkylcarbonyl or aminocarbonyl； carbonylalkyl substituted with a hydroxy, alkoxy or hiroxyalkylamino； carbonyl substituted with a hydroxy, morpholino, alkoxy, hydroxyalkylaminoalkoxy or cyclohexyloxycarbonyloxyalkoxy； carbonylamino substituted with an alkyl or alkoxy； and aminocarbonyl optionally substituted with one or two substituents selected from amino, hydroxy, alkoxy, alkenyl and alkyl (optionally substituted with a halogen, thiol, piperidino, amino, alkoxy, alkoxycarbonyl or aminocarbonyl, or with one or two hydroxy groups)； R2 is selected from H, cyano, alkoxy, halogen； acrylic acid or an alkyl or hydroxyalkylamide ester thereof； alkyl substituted with a hydroxy or piperidino, carbonylalkyl substituted with a hydroxy, alkoxy (optionally substituted with a cyclohexyloxycarbonyloxy), piperidino or hydroxyalkylamino； carbonyl substituted with a hydroxy, alkoxy or hydroxyalkylamino； carbonylalkoxy substituted with a hydroxy or alkoxy； and carbonylalkyl sulfanyl substituted with a hydroxy or alkoxy； R3 is H or a substituent selected from alkyl optionally substituted with a carboxy, cyano, pyrrolidyl, piperidino, alkoxy, alkylsulfanyl, or with one or two hydroxy groups； carbonyl substituted with an alkyl or alkoxy； carbonylalkoxyalkyl substituted with a hydroxy or alkoxy； carbonylalkyl substituted with an alkyl, alkoxy or alkylphenyl； and aminoalkyl substituted with an aminocarbonyl or alkanesulfonyl； where one of R1 and R2 is not H； the dashed line represents a single bond or a double bond, A is not substituted or is oxo, B is C or O； and one of X and Y is C and the other is S； with the proviso that if R2 is halogen or alkoxy, then R1 is not H, A is not substituted and B is O.Un
