A series of new N-(1,5-benzodiazepin-3-yl)-N′-arylureas, 2, bearing an alkyl substituent at the N5 position of the benzodiazepine nucleus has been studied as potential CCK-B antagonists. The homochiral compounds were obtained by resolving their precursors (amines 4) with a new resolution method based on the reaction between the amines and the chiralauxiliary5, the subsequent separation of the diastereomers