Synthesis and structure–activity relationship studies of polysubstituted pyrimidines as inhibitors of immune-activated nitric oxide production

Based on the previous discovery of the inhibitory effect of the 5-substituted 2-amino-4,6-dichloropyrimidines on nitric oxide (NO) production in vitro, a series of novel pyrimidine derivatives, namely 4,6-dichloro-2-[( N , N -dimethylamino)methyleneamino]pyrimidines, 2,4-diamino-6-chloropyrimidines, and 2,4-diamino-6-(2-hydroxyethoxy)pyrimidines, were prepared bearing various substituents at the C-5 position on the pyrimidine, such as hydrogen, methyl, ethyl, propyl, isopropyl, propargyl, allyl, butyl, sec -butyl, phenyl, benzyl, and fluorine. The intrinsic biological potential of the prepared compounds was characterized by effects on the in vitro production of immune-activated NO in mouse peritoneal cells. All 5-substituted 4,6-dichloro-2-[( N , N -dimethylamino)methyleneamino]pyrimidines strongly inhibited NO production. The IC 50 s were <5 µM in most cases. The highest inhibitory activity was observed for the 5- sec -butyl analog (IC 50 = 2.57 µM), the lowest one for 5-unsubtituted compound (IC 50 = 11.49 µM). With the exception of the 5-fluoro-4,6-dichloro-2-[( N , N -dimethylamino)methyleneamino] derivative, all other compounds were devoid of cytotoxic effects. The hitherto obtained data suggest that the NO-inhibitory activity depends on the presence of the 2-amino-4,6-dichloropyrimidine scaffold.