In the title compound, C(18)H(16)N(4)O(2), the plane defined by the ethyl C atoms and the attached N atom is inclined to the adjacent pyridine ring at an angle of 67.87 (16)°. The dihedral angle between the two heterocyclic rings is 3.33 (16)°. The mol-ecular conformation is stabilized by an intra-molecular N-H⋯O hydrogen bond and the crystal structure by inter-molecular C-H⋯O hydrogen bonds, f...

The title compound, C(14)H(15)N(3)O(2), was prepared by the reaction of 4-(dimethyl-amino)-benzaldehyde and furan-2-carbohydrazide. The dihedral angle between the benzene ring and the furan ring is 25.59 (19)°. In the crystal, mol-ecules are linked by inter-molecular N-H⋯O hydrogen bonds, forming chains along [010].

The title compound, C(13)H(9)N(3)OS, was prepared by the reaction of thio-phene-2-carbohydrazide and 4-formyl-benzonitrile. The dihedral angle between the benzene and thio-phene rings is 11.9 (1)°. In the crystal structure, mol-ecules are linked into centrosymmetric dimers by pairs of N-H⋯O hydrogen bonds.

The title compound, C(11)H(13)N(3)O, is a derivative of the anti-tuberculosis drug isoniazid [systematic name: pyridine-4-carbohydrazide]. The crystal structure consists of repeating hydrogen-bonded chains parallel to the b axis. Adjacent mol-ecules in the chains are linked by bifurcated N-H⋯(O,N) hydrogen bonds, which form an R(1) (2)(5) ring motif.

The carbohydrazide 1 was used as the precursor for the synthesis of a number of new aromatic C-nucleosides containing 1,3,4-oxadiazole 7, [1,3,4]oxadiazolo[2,3-a]isoindole 10b and pyrazole units 18. On the other hand, the thiosemicarbazone 20 was used as the key intermediate for synthesis of 1,3,4-oxadiazole  and 1,2,4-triazole-3-thione derivatives 21 and 23. The antioxidant activities of the p...