A compound which is represented by Formula (I): ##STR88## wherein R1 is a lower alkyl, cycloalkyl, cycloalkyl-lower alkyl, aryl or aralkyl group which is optionally substituted,R2 is a group represented by the formula: --COOR': (wherein R' is a lower alkyl or aralkyl which is optionally substituted), lower alkyl or halogenated lower alkyl, or, R1 and R2, together with adjacent carbonyl group, form