Crystal structures of ()-2-amino-4-methyl-sulfanyl-6-oxo-1-(1-phenyl-ethyl-idene-amino)-1,6-di-hydro-pyrimidine-5-carbo-nitrile and ()-2-amino-4-methyl-sulfanyl-6-oxo-1-[1-(pyridin-2-yl)ethyl-idene-amino]-1,6-di-hydro-pyrimidine-5-carbo-nitrile.

The title compounds , CHNOS, and , CHNOS, both show an configuration about the N=C bond and a planar NH group. The mol-ecules, which only differ in the presence of a phenyl (in ) or pyridyl (in ) substituent, are closely similar except for the different orientations of these groups. The amino hydrogen atoms form classical hydrogen bonds; in the acceptors are the oxygen atom and the cyano nitro-gen atom, leading to ribbons of mol-ecules parallel to the axis, whereas in the acceptors are the oxygen atom and the pyridyl nitro-gen, leading to a layer structure perpendicular to (01).