Abstract
A series of novel nopol derivatives bearing the 1,3,4-thiadiazole-thiourea moiety were designed and synthesized by multi-step reactions in search of potent natural product-based antifungal agents. Their structures were confirmed by FT-IR, NMR, ESI-MS, and elemental analysis. Antifungal activity of the target compounds was preliminarily evaluated by in vitro methods against Fusarium oxysporum f. sp. cucumerinum, Cercospora arachidicola, Physalospora piricola, Alternaria solani, Gibberella zeae, Rhizoeotnia solani, Bipolaris maydis, and Colleterichum orbicalare at 50 µg/mL. All the target compounds exhibited better antifungal activity against P. piricola, C. arachidicola, and A. solani. Compound 6j (R = m, p-Cl Ph) showed the best broad-spectrum antifungal activity against all the tested fungi. Compounds 6c (R = m-Me Ph), 6q (R = i-Pr), and 6i (R = p-Cl Ph) had inhibition rates of 86.1%, 86.1%, and 80.2%, respectively, against P. piricola, much better than that of the positive control chlorothalonil. Moreover, compounds 6h (R = m-Cl Ph) and 6n (R = o-CF3 Ph) held inhibition rates of 80.6% and 79.0% against C. arachidicola and G. zeae, respectively, much better than that of the commercial fungicide chlorothalonil. In order to design more effective antifungal compounds against A. solani, analysis of the three-dimensional quantitative structure–activity relationship (3D-QSAR) was carried out using the CoMFA method, and a reasonable and effective 3D-QSAR model (r2 = 0.992, q2 = 0.753) has been established. Furthermore, some intriguing structure–activity relationships were found and are discussed by theoretical calculation.
Highlights
Turpentine oil, which was obtained by the steam distillation of the oleoresin exudate from living pine trees, is an extremely abundant natural biomass resource in nature, and is widely used in the synthesis of fine chemicals such as food additives, pharmaceuticals, agrochemicals, and flavors [1]
With the chemical name of 2-(6,6-dimethyl-2-bicyclo [3.1.1] hept-2-enyl) ethanol, is an optically active bicyclic primary alcohol, and contains three reactive functional groups, including a hydroxyl group, a carbon–carbon double bond, and a four-membered ring. It is usually prepared by a Prins condensation reaction of β-pinene with paraformaldehyde and is generally used in the flavor and fragrance industries, in the agrochemical industry to produce pesticides, as well as in the manufacture of soaps, detergents, polishes, and other household products [3]
The strong absorption bands at 1524–1586 cm−1 and the moderate absorption bands at 646–660 cm−1 were assigned to the vibrations of C=N and C–S–C in 1,3,4-thiadiazole moiety, respectively
Summary
Turpentine oil, which was obtained by the steam distillation of the oleoresin exudate from living pine trees, is an extremely abundant natural biomass resource in nature, and is widely used in the synthesis of fine chemicals such as food additives, pharmaceuticals, agrochemicals, and flavors [1]. With the chemical name of 2-(6,6-dimethyl-2-bicyclo [3.1.1] hept-2-enyl) ethanol, is an optically active bicyclic primary alcohol, and contains three reactive functional groups, including a hydroxyl group, a carbon–carbon double bond, and a four-membered ring. It is usually prepared by a Prins condensation reaction of β-pinene with paraformaldehyde and is generally used in the flavor and fragrance industries, in the agrochemical industry to produce pesticides, as well as in the manufacture of soaps, detergents, polishes, and other household products [3]. 5a-cntioviptyyrle-la2t-ioanmshiipnsoo-f1th,3e ,ti4tl-etchoimapdoiuanzdos wleer(e5d)e.teLrmaisnteldya,saweslel.ries of target comp th2.eRseiszueltds abndyDthisceunssuiocnleophilic addition reaction of compound 5 with di
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