2,6-Di(4-pyridyl)-4-oxo-piperidin-3,5-dicarbonsaeurediethylester;2.6-Di-pyridyl-(4)-piperidon-(4)-dicarbonsaeure-(3.5)-diethylester;2,6-Di-
-piperidon-(4)-dicarbonsaeure-(3,5)-diethylester;4'-oxo-1',2',3',4',5',6'-hexahydro-[4,2';6',4'']terpyridine-3',5'-dicarboxylic acid diethyl ester