| abstract |
A compound of the formula :n n whereinn R¹ is aryl which may be substituted with halogen, nitro, amino, lower alkylamino, lower alkoxy or acylamino, R² is hydrogen; alkyl; cycloalkyl; or lower alkyl which is substituted with cyclo(lower)alkyl, cyclo(lower)alkenyl, a heterocyclic group or aryl optionally substituted with substituent(s) selected from the group consisting of halogen, hydroxy and lower alkoxy; R³ is hydrogen, lower alkyl or aryl which may be substituted with halogen, nitro, amino or lower alkylamino, R⁴ is hydrogen, halogen, lower alkyl, lower alkoxy or aryl which may be substituted with halogen, R⁵ is hydrogen, halogen, lower alkyl or aryl, A is a single bond or lower alkylene, and X is O, S or NH, nprovided that R³ is aryl which may be substituted with halogen, nitro, amino or lower alkyamino, or R⁴ is halogen, lower alkoxy or aryl which may be substituted with halogen, nwhen R² is cycloalkyl, and pharmaceutically acceptable salts thereof, processes for their preparation and pharmaceutical compositions comprising them. |