2-amino-6-ethyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carbonitrile synthesis, coupling with salicylaldehyde derivatives; synthesis, structural characterization of the Ni(II), Cu(II) and Zn(II) complexes, and investigation of their some biological activities

In this work firstly, the compound "2-amino-6-ethyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carbonitrile" (I), which is an aminothiophene derivative was obtained according to literature method. In the second step, as a result of the condensation reaction of the compound (I) with the compound "3,5,-dichloro-2-hydroxybenzaldehyde", a salicylaldehyde derivative, "2-((3,5-dichloro-2-hydroxybenzylidene) amino)-6-ethyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carbonitrile" new Schiff base ligand (L) was synthesised. In the third step, the original L-Ni(II), L-Cu(II) and L-Zn(II) complexes of the new Schiff base ligand (L) were synthesized. The structure of the ligand (L) was clarified by FT-IR, 1H NMR, 13C NMR and elemental analysis methods. The chemical structures of the complexes were characterized by spectroscopic methods such as FT-IR, UV-visible region and LC-MS mass analysis, as well as TGA-DTA analysis, magnetic susceptibility and elemental analysis. It was determined that the Schiff base (L) acts as a bidentate ligand in the mononuclear L-Ni(II) and L-Zn(II) complexes, whereas it acts as a tridentate ligand in the binuclear L-Cu(II) complex. Therefore, the octahedral geometry for the L-Ni(II) and L-Zn(II) complexes; the square pyramidal geometry was proposed for the L-Cu(II) complex. Finally, the antioxidant activities of Schiff base ligand (L) and it's complexes and the inhibitory effects against the AChE enzyme were examined. The experimental results of enzyme inhibition studies were supported by molecular docking study of the ligand.