Heterocyclic compounds

A heterocyclic compound represented by the formula:

• ##STR77## wherein R.sup.1 represents a C.sub.1 -C.sub.6 alkanoyl group;
• R.sup.2 represents a lower alkyl group;
• Het represents a pyridine ring;
• R.sup.3 represents a carboxy group, an amino group, a lower alkylamino group, a carboxy lower alkylamine group, a lower alkanoylamino group, a carboxy lower alkanoylamino group, a di-lower alkylamino group, a hydroxy group, a lower alkoxy group, a carboxy lower alkoxy group, a mercapto group, a lower alkylthio group, a carboxy lower alkylthio group, a group represented by the formulas:
• ##STR78## wherein p represents an integer of 1 to 5, q represents 0, 1 or 2, r represents an integer of 1 to 5;
• R.sup.4 represents a carboxy group, a lower alkoxy group, a carboxy lower alkoxy group, a lower alkyl group, or a carboxyl lower alkyl group and each, except for the carboxy group, may have a sulfur atom or an oxygen atom between two carbon atoms in the carbon chain thereof);
• provided that when the compound is substituted by a carboxy group, said carboxy group may be in the form of a lower alkyl ester, a phenyl lower alkyl ester, a lower alkoxy phenyl lower alkyl ester, or a pharmacologically acceptable non-toxic acid addition salt.