A compound of the following general formula :

wherein

X is carbonyl or sulfonyl;
Y is bond or lower alkylene;
R¹ is halogen, lower alkyl, halo(lower)alkyl, aryloxy, nitro or amino which may have 1 or 2 and same or different substituent(s) selected from lower alkyl, acyl and lower alkanesulfonyl;
R² is aryl or an aromatic hetero(mono- or bi-)cyclic group, and each of which may have 1, 2 or 3 suitable substituent(s);
R³ is hydrogen or lower alkyl;
R⁴ is

(i) a group of the formula -SO₂-R⁵ in which R⁵ is lower alkyl or aryl optionally substituted with lower alkyl or lower alkoxy,
(ii) a group of the formula
in which R⁶ is aryl optionally substituted with lower alkyl or lower alkoxy, or
(iii) a group of the formula -A-(Z) p in which
A  is bond, lower alkylene, lower alkenylene or lower alkynylene,
Z  is hydrogen, halogen, hydroxy, nitrile, amino, cyclo(lower)alkyl, aryl, aryloxy, acyl, acylamino, lower alkanesulfonylamino, arylsulfonylamino or an aromatic hetero(mono- or bi-)cyclic group, and each of the cyclic group may have 1, 2 or 3 suitable substituent(s), and
p  is 1, 2 or 3; and

n is 0, 1 or 2;

provided that when n or p is more than 1, these R¹ and Z may be the same or different group respectively; or its pharmaceutically acceptable salt, processes for their preparation and pharmaceutical compositions comprising them.