Novel compounds exhibiting good inhibitory activity versus Dipeptidyl Peptidase-IV(DPP-IV) include those of the following formula (1) or pharmaceutically acceptable salt thereof: wherein A is a substituted or unsubstituted 1,4,5,7-tetrahydro-pyrazolo[3,4-c]pyridine, 5,6 -dihydro-8H-[1,2,4]triazolo[4,3-a]pyrazine, 4,5-dihydro-7H-isooxazolo[3,4-c]pyridine, 3,4 -dihydroisoquinoline, 5,8-dihydropyrido[3,4-d]pyrimidine, or 6,7 -dihydro[1,3]thiazolo[4,5,c]pyridine, and B is a substituted or unsubstituted piperidin-2-one, morpholin-3-one, oxazolidin-2-one, pyrrolidin-2-one, or 1,5-dihydro-pyrrol-2-one. Methods of preparing the novel inhibitory compounds of formula (1) and pharmaceutical compositions containing the same as an active agent are disclosed.