New isoxazole(3,5)substituted thiosemicarbazone: Synthesis, crystal structure and spectroscopic studies of the binding mode to protein and calf thymus DNA

Abstract Six new 3,5-isoxazole thiosemicarbazone derivatives (ITCs) ( HL1 – HL6 ) were synthesized and characterized using microanalysis, spectroscopic methods and for HL2 , HL3 , HL5 and HL6a by a single crystal X-ray diffraction. The combined analyses, utilizing NMR and X-ray techniques, showed that the compounds presented an E conformation both in solution and solid state. The intermolecular N3 H3N···S1 hydrogen bonds, between the thiosemicarbazone groups, resulted in rings for all crystals. For HL2 and HL5, one medium strength (N4 H4N···S1) and one weak (C8 H8···N1) intermolecular hydrogen bond was also observed. HL3 presented a π(ar)- π(ar) stacking interaction and HL6a was stabilized by three hydrogen bonds involving DMSO oxygen. The interconnections in the crystal structures were analyzed using Hirshfeld surfaces. The interaction studies, using fluorescence and absorbance spectroscopy, showed that the ITCs interacted with DNA and human serum albumin (HSA).