Novel indazole Schiff base metal chelates as potential antifungal agents: synthesis, characterization, and computational analysis

Soil-borne phytopathogenic fungi pose a significant risk to many economically important crops due to their ability to survive in the soil for extended periods without a host. Thus, a novel Schiff base (HL), 3-(1H-indazol-5-ylimino)-1-phenylbut-1-en-1-ol, was synthesized by the condensation of 5-aminoindazole with benzoyl acetone. Its Co²⁺, Ni²⁺, and Cu²⁺ chelates were also synthesized. These compounds were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, UV–Vis, EI–mass spectroscopy, XRD, TGA, magnetic susceptibility, elemental analysis, and molar conductance. The ligand possesses an enol form and functions as a monobasic bidentate through the deprotonated OH and C=N groups. The Co²⁺ and Ni²⁺ ions produced 1:1 (M:L) chelates, whereas Cu²⁺ ion produced a 1:2 (M:L) chelate. From the characterization results and the DFT method, it was revealed that the Co²⁺ chelate has tetrahedral geometry, while Ni²⁺ and Cu²⁺ chelates are octahedral. The antifungal activities of the ligand and the metal chelates were evaluated against some plant pathogenic fungi, namely, Stromatinia cepivora, Botrytis allii, Rhizoctonia solani, and Sclerotinia sclerotiorum in comparison with the commercial fungicide Tebuconazole. The Ni⁺² chelate emerged as the most potent agent that achieved 100% inhibition for the S. cepivora and S. sclerotiorum. It also caused significant morphological alterations in S. sclerotiorum as revealed by the SEM micrograph. The treated S. sclerotiorum hyphae displayed irregular, shriveled, and collapsed structures in contrast to the smooth and robust appearance of the control. The molecular docking study further confirmed that Ni²⁺ chelate strongly interacted with the active site of CYP51 protein compared with Co²⁺ and Cu²⁺ chelates and the fungicide Tebuconazole. The superior efficacy of Ni²⁺ chelate offers a promising alternative to traditional fungicides.

Graphical Abstract