Planarity of heteroaryldithiocarbazic acid derivatives showing tuberculostatic activity. II. Crystal structures of 3-[amino(pyrazin-2-yl)methylidene]-2-methylcarbazic acid esters.

Four compounds showing moderate antituberculostatic activity have been studied to test the hypothesis that the planarity of the 2-[amino(pyrazin-2-yl)methylidene]dithiocarbazate fragment is crucial for activity. N'-Anilinopyrazine-2-carboximidamide, C(11)H(11)N(5), D1, and diethyl 2,2'-[({[amino(pyrazin-2-yl)methylidene]hydrazinylidene}methylidene)bis(sulfanediyl)]diacetate, C(14)H(19)N(5)O(4)S(2), B1, maintain planarity due to conjugation and attractive intramolecular hydrogen-bond contacts, while methyl 3-[amino(pyrazin-2-yl)methylidene]-2-methyldithiocarbazate, C(8)H(11)N(5)S(2), C1, and benzyl 3-[amino(pyrazin-2-yl)methylidene]-2-methyldithiocarbazate, C(14)H(15)N(5)S(2), C2, are not planar, due to methylation at one of the N atoms of the central N-N bond. The resulting twists of the two molecular halves (parts) of C1 and C2 are indicated by torsion angles of 116.5 (2) and -135.9 (2)°, respectively, compared with values of about 180° in the crystal structures of nonsubstituted compounds. As the methylated derivatives show similar activity against Mycobacterium tuberculosis to that of the nonsubstituted derivatives, maintaining planarity does not seem to be a prerequisite for activity.