In order to understand the antifungal activity of some derivatives of sanguinarine (S) and chelerythrine (C) and their structure-activity relationships, sixteen derivatives of S and C were prepared and evaluated for in vitro antifungal activity against seven phytopathogenic fungi by the mycelial growth rate method. The results showed that S, C and their 6-alkoxy dihydro derivatives S₁–S ₄, C₁–C ₄ and 6-cyanodihydro derivatives S₅, C₅ showed significant antifungal activity at 100 µg/mL against all the tested fungi. For most tested fungi, the median effective concentrations of S, S₁, C and C₁ were in a range of 14–50 µg/mL. The structure-activity relationship showed that the C=N⁺ moiety was the determinant for the antifungal activity of S and C. S₁–S₅ and C₁–C₅ could be considered as the precursors of S and C, respectively. Thus, the present results strongly suggested that S and C or their derivatives S₁–S₅ and C₁–C₅ should be considered as good lead compounds or model molecules to develop new anti-phytopathogenic fungal agents.

The title compounds are a class of structurally simple analogues of quaternary benzo[c]phenanthridine alkaloids (QBAs). In order to develop novel QBA-like antifungal drugs, in this study, 24 of the title compounds with various substituents on the N-phenyl ring were evaluated for bioactivity against seven phytopathogenic fungi using the mycelial growth rate method and their SAR discussed. Almost all the compounds showed definite activities in vitro against each of the test fungi at 50 μg/mL and a broad antifungal spectrum. In most cases, the mono-halogenated compounds 2–12 exhibited excellent activities superior to the QBAs sanguinarine and chelerythrine. Compound 8 possessed the strongest activities on each of the fungi with EC₅₀ values of 8.88–19.88 µg/mL and a significant concentration-dependent relationship. The SAR is as follows: the N-phenyl group is a high sensitive structural moiety for the activity and the characteristics and position of substituents intensively influence the activity. Generally, electron-withdrawing substituents remarkably enhance the activity while electron-donating substituents cause a decrease of the activity. In most cases, ortha- and para-halogenated isomers were more active than the corresponding m-halogenated isomers. Thus, the title compounds emerged as promising lead compounds for the development of novel biomimetic antifungal agrochemicals. Compounds 8 and 2 should have great potential as new broad spectrum antifungal agents for plant protection.

A series of 3-aryl propionic esters and their analogues were designed and evaluated for acaricidal activity in vitro against Psoroptes cuniculi, a mange mite. The structure–activity relationship (SAR) was also discussed. The results showed that 6 compounds possessed the excellent activity (LC₅₀ = 0.17–0.24 mM, LT₅₀ = 1.5–2.9 h), superior to ivermectin (LC₅₀ = 0.28 mM, LT₅₀ = 8.9 h) (P < 0.05), a standard drug. Furthermore, 7 compounds showed the good activity (LC₅₀ = 0.25–0.37 mM, LT₅₀ < 3.9 h), slightly lower or close to that of ivermectin. One compound displayed super-fast acaricidal property, far superior to ivermectin. SAR analysis found that the ester group is vital for the activity and the small steric hindrance adjacent to the ester group is advantageous for the high activity. The <C4 linear alcohol esters can give the higher activity. The substituents on the 3-phenyl ring or replacement of the 3-phenyl with heterocyclic aryl generally decreases the activity. The position of the ester group in the ester chain also influences the activity, where the 3-phenyl propionate and the benzoate had the highest and lowest activity, respectively. Thus, 3-arylpropionates emerged as new and promising high-efficient acaricide candidates.

Thirty new title compounds along with five known analogues were prepared from commercially available 2-arylhydrazin-1-ium chlorides and α-ketoglutaric acid. The mycelium growth rate method was used to evaluate inhibition activity against six strains of plant pathogenic fungi. Most of the compounds displayed the activity for each the fungi at 150 μΜ, higher than azoxystrobin, a positive drug. Compound 6-2 showed the lowest average IC₅₀ value of 4.58 μg/mL for all the fungi where F. solani exhibited the highest susceptibility to most of the compounds. For F. solani, some compounds were more active with IC₅₀ values of 2.67–8.48 μM than thiabendazole (IC₅₀ = 9.30 μM) and/or carbendazim (IC₅₀ = 3.36 μM). The SAR showed that the activity is significantly affected by substituents on the A-ring and/or D-ring along with the degree of unsaturation of the C-ring. Thus, a series of new β-carboline compounds with potent antifungal potential were found.