: Since the discovery of the multi-drug resistance (MDR) phenotype, reversant agents of various origins and structures have been extensively studied. In the present work, two series of related 2,4,6-tris(amino)-striazines with di †erent MDR potential1 were studied by 15N NMR spectroscopy. The 15N nucleus allows an easy identiÐcation of two protonation sites and an estimation of the electronic e †ects. 15N was further found to be well suited to demonstrate the occurrence at room temperature of restricted rotation around the ArÈN bonds between the amino substituents and the s-triazine ring and to measure the rotational barriers. Crystal structures were determined by x-ray analysis of the compounds at various stages of protonation. The e †ects of the protonation at the sterically less hindered nitrogen of the triazine, detected by the NMR study, were conÐrmed in the solid-state structures. In the crystals, the orientation of the NÈH and NÈC bonds of the NHallyl substituent with respect to the triazine ring does not depend on the protonation state and corresponds to one of the conformations postulated in solution.

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