A versatile approach to hybrid thiadiazine-based molecules by the Ugi four-component reaction

Identification of novel thiadiazin derivatives as potentially selective inhibitors towards trypanothione reductase from Trypanosoma cruzi by molecular docking using the numerical index poses ratio Pr and the binding mode analysis

Abstract

Chagas disease is a serious health problem in Central and South America for which effective treatment is not currently available. This illness is caused by the protozoa Trypanosoma cruzi, a species that relies on a thiol-based metabolism to regulate oxidative stress. Trypanothione reductase enzyme plays a central role in the metabolic pathway of the parasite. In this work, a virtual screening of a library of novel thiadiazine derivatives against trypanothione reductase using molecular docking was performed. Four different series of hybrid ligands having in the structure one or two peptoid moieties (series I and II) or the tetrazole ring (series III and IV) were considered. An ad hoc numerical index called poses ratio was introduced to interpret the results of the docking analysis and to establish relevant structure-interaction relationships. In addition, six binding modes were found for the ligands with the highest populated conformational clusters after applying contact-based analysis. The most regular and relevant were binding modes I and II, found mainly for ligands from series I. A subsequent molecular docking on human glutathione reductase enzyme allowed to assess the possible cytotoxicity of the ligands towards human cells. A selective binding profile was found for ligands with interactions in the Hydrophobic cleft, the spermidine and the Z subsites inside the active site of trypanothione reductase. At the end of the study, new thiadiazine-based compounds were identified as plausible candidates to selectively inhibit the parasitic enzyme.

Graphic abstract

Design, synthesis and antimicrobial activities of novel 1,3,5-thiadiazine-2-thione derivatives containing a 1,3,4-thiadiazole group

A series of novel 1,3,5-thiadiazine-2-thione derivatives containing a 1,3,4-thiadiazole group was designed and synthesized. The structures of all the compounds were well characterized using ¹H NMR, ¹³C NMR and high-resolution mass spectrometer, and further confirmed by the X-ray diffraction analysis of 8d. The antimicrobial activities of all the target compounds against Xanthomonas oryzae pv. oryzicola, X. oryzae pv. oryzae, Rhizoctonia solani and Fusarium graminearum were evaluated. The in vitro antimicrobial bioassays indicated that some title compounds exhibited noteworthy antimicrobial effects against the above strains. Notably, the compound N-(5-(ethylthio)-1,3,4-thiadiazol-2-yl)-2-(5-methyl-6-thioxo-1,3,5-thiadiazinan-3-yl)acetamide (8a) displayed obvious antibacterial effects against X. oryzae pv. oryzicola and X. oryzae pv. oryzae at 100 μg/mL with the inhibition rates of 30% and 56%, respectively, which was better than the commercial bactericide thiodiazole-copper. In addition, the anti-R. solani EC₅₀ value of 8a was 33.70 μg/mL, which was more effective than that of the commercial fungicide hymexazol (67.10 μg/mL). It was found that the substitutes in the 1,3,5-thiadiazine-2-thione and the 1,3,4-thiadiazole rings played a vital role in the antimicrobial activities of the title compounds. More active title compounds against phytopathogenic microorganisms might be obtained via further structural modification.

Design and synthesis of novel 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N'-phenylacethydrazide derivatives as potential fungicides

A series of novel 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N'-phenylacethydrazide derivatives were designed, synthesized and evaluated for their antifungal activities against Fusarium graminearum (Fg), Rhizoctonia solani (Rs), Botrytis cinerea (Bc) and Colletotrichum capsici (Cc). The bioassay results in vitro showed that most of the title compounds exhibited impressive antifungal activities against the above plant fungi. Particularly, the compounds 5c, 5f, 5g, 5i, 5m and 5p displayed desirable anti-Rs activities, with the corresponding EC₅₀ values of 0.37, 0.32, 0.49, 0.50, 0.46 and 0.45 µg/mL, respectively, which are superior to the positive control carbendazim (0.55 µg/mL). Further in vivo bioassay results showed that the anti-Rs activity of title compound 5f at 200 µg/mL reached 95.84% on detached rice leaves and 93.96% on rice plants. Featuring convenient synthesis, novel structures and desirable antifungal activity, these 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N'-phenylacethydrazide derivatives could be further studied as the potential candidates of novel agricultural fungicides.