and MN19, characterized by rings with different size, have been prepared and evaluated for their nootropic activity in the mouse passive-avoidance test. It was found that the optimal ringsize for the analogs of DM235, showing endocyclic both amidic groups, is 6 or 7 atoms. For the compounds structurally related to MN19, carrying an exocyclic amide group, the piperidine ring is the moiety which gives