A series of novel pyrazole amide derivatives were designed and synthesized by multi-step reactions from phenylhydrazine and ethyl 3-oxobutanoate as starting materials, and their structures were characterized by NMR, MS and elemental analysis. The antifungal activity of the title compounds was determined. The results indicated that some of title compounds exhibited moderate antifungal activity. Furthermore, DFT calculations were used to study the structure-activity relationships (SAR).

The increasing prevalence of multi-drug resistant fungal infections has encouraged the search for new antifungal agents. Hydrazone derivatives always exhibited diversity activities, including antifungal, anti-inflammatory, anti-oxidation, anti-cancer activity. Regarding the heterocyclic moiety, 1,2,4-triazolo[4,3-a]pyridine derivatives also display broad activities, such as antifungal activity, anticonvulsant activity, herbicidal activity, antimicrobial activity and anticancer activity. A series of novel 1,2,4-triazolo[4,3-a]pyridine derivatives containing hydrazone moiety were designed and synthesized from 2,3-dichloropyridine, hydrazine hydrate by multi-step reactions under microwave irradiation condition, and their structures were characterized by FT IR, 1H NMR, 13C NMR, 19F NMR, MS and elemental analysis. The antifungal activities of title compounds were determined. The results indicated that some of the title compounds exhibited good antifungal activity. Furthermore, DFT calculation was carried out for studying the structure–activity relationship (SAR). A practical synthetic route to obtain 1,2,4-triazolo[4,3-a]pyridine derivatives is presented. This study suggests that the 1,2,4-triazolo[4,3-a]pyridine derivatives exhibited good antifungal activity.

8-chloro-3-((3-chlorobenzyl)thio)-[1,2,4]triazolo[4,3-a]pyridine was synthesized and recrystallized from EtOH. The compound was characterized by ¹H NMR, ¹³C NMR, FTIR, MS, elemental analysis and X-ray diffraction. The compound was crystallized in the monoclinic space group P2(1)/c with a = 8.1992(5), b = 21.7731(12), c = 7.8454(6) Å, α = 90, β = 108.421(7), γ = 90°, V = 1328.81 (15)ų, Z = 4 and R = 0.0351. Theoretical calculation of the title compound was carried out with B3LYP/6-31G. The full geometry optimization was carried out by using the 6-31G basis set. The frontier orbital energy and atomic net charges were discussed. The experimental results of the compound have been compared with theoretical results and it was found that the experimental data shows good agreement with the calculated values.

The title compound 4-(5-((4-bromobenzyl)thio)-4-phenyl-4H-1,2,4-triazol-3-yl)pyridine (C₂₀H₁₅BrN₄S) was synthesized, and its structure was confirmed by ¹H NMR, MS and elemental analyses and single-crystal X-ray structure determination. It crystallizes in the triclinic space group P-1 with a = 7.717(3), b = 9.210(3), c = 13.370(5) Å, α = 80.347(13), β = 77.471(13), γ = 89.899(16)°, V = 913.9(6) ų, Z = 2 and R = 0.0260 for 3145 observed reflections with I > 2σ(I). A Density functional theory (DFT) (B3LYP/6-31G) calculation of the title molecule was carried out. The full geometry optimization was carried out using a 6-31G basis set, and the frontier orbital energy. Atomic net charges are discussed. Calculated bond lengths and bond angles were found to differ from experimental values, and the compound exhibits moderate antifungal activity.