Combined Application of Tacrolimus with Cyproconazole, Hymexazol and Novel {2-(3-R-1H-1,2,4-triazol-5-yl)phenyl}amines as Antifungals: In Vitro Growth Inhibition and In Silico Molecular Docking Analysis to Fungal Chitin Deacetylase.

Agents with antifungal activity play a vital role as therapeutics in health care, as do fungicides in agriculture. Effectiveness, toxicological profile, and eco-friendliness are among the properties used to select suitable substances. Furthermore, a steady supply of new agents with different modes of action is required to counter the well-known potential of human and phyto-pathogenic fungi to develop resistance against established antifungals. Here, we use an in vitro growth assay to investigate the activity of the calcineurin inhibitor tacrolimus in combination with the commercial fungicides cyproconazole and hymexazol, as well as with two earlier reported novel {2-(3-R-1H-1,2,4-triazol-5-yl)phenyl}amines, against the fungi Aspergillus niger, Colletotrichum higginsianum, Fusarium oxysporum and the oomycete Phytophthora infestans, which are notoriously harmful in agriculture. When tacrolimus was added in a concentration range from 0.25 to 25 mg/L to the tested antifungals (at a fixed concentration of 25 or 50 mg/L), the inhibitory activities were distinctly enhanced. Molecular docking calculations revealed triazole derivative 5, (2-(3-adamantan-1-yl)-1H-1,2,4-triazol-5-yl)-4-chloroaniline), as a potent inhibitor of chitin deacetylases (CDA) of Aspergillus nidulans and A. niger (AnCDA and AngCDA, respectively), which was stronger than the previously reported polyoxorin D, J075-4187, and chitotriose. The results are discussed in the context of potential synergism and molecular mode of action.

Novel N-Cycloalkylcarbonyl-N'-arylthioureas: Synthesis, Design, Antifungal Activity and Gene Toxicity.

A synthesis method of novel N-cycloalkylcarbonyl-N'-arylthioureas was developed. It consists of sequential addition of equimolecular amounts of ammonium isothiocyanate and substituted anilines to cycloalkylcarbonyl chlorides. The identity and purity of products were confirmed by LC/MS spectra, their structure by elemental analysis, IR and 1 H-NMR spectra. Preliminary antimicrobial screening for standard microorganisms and molecular docking allowed to select several structures for antifungal and genetic toxicity studies. Conducted in vitro screening of 9 compounds for antifungal potential against 11 phytopathogenic fungi and three Phytophthora strains revealed that two N-(arylcarbamothioyl) cyclopropanecarboxamides at a concentration of 50 µg/ml exhibited activities comparable to the standard antifungal agent 'Cyproconazole'. Analysis of mutagenicity of novel thioureas using the Salmonella reverse mutagenicity assay ('Ames Test') showed a low gene-toxicity profile.

Synthesis and mode of action studies of novel {2-(3-R-1H-1,2,4-triazol-5-yl)phenyl}amines to combat pathogenic fungi.

Due to their high specificity and efficacy, triazoles have become versatile antifungals to treat fungal infections in human healthcare and to control phytopathogenic fungi in agriculture. However, azole resistance is an emerging problem affecting human health as well as food security. Here we describe the synthesis of 10 novel {2-(3-R-1H-1,2,4-triazol-5-yl)phenyl}amines. Their structure was ascertained by liquid chromatography-mass spectrometry, 1 H and 13 C NMR, and elemental analysis data. Applying an in vitro growth assay, these triazoles show moderate to significant antifungal activity against the opportunistic pathogen Aspergillus niger, 12 fungi (Fusarium oxysporum, Fusarium fujikuroi, Colletotrichum higginsianum, Gaeumannomyces graminis, Colletotrichum coccodes, Claviceps purpurea, Alternaria alternata, Mucor indicus, Fusarium graminearum, Verticillium lecanii, Botrytis cinerea, Penicillium digitatum) and three oomycetes (Phytophtora infestans GL-1, P. infestans 4/91; R+ and 4/91; R-) in the concentration range from 1 to 50 µg/ml (0.003-2.1 µM). Frontier molecular orbital energies were determined to predict their genotoxic potential. Molecular docking calculations taking into account six common fungal enzymes point to 14α-demethylase (CYP51) and N-myristoyltransferase as the most probable fungal targets. With respect to effectiveness, structure-activity calculations revealed the strong enhancing impact of adamantyl residues. The shown nonmutagenicity in the Salmonella reverse-mutagenicity assay and no violations of drug-likeness parameters suggest the good bioavailability and attractive ecotoxicological profile of the studied triazoles.

Tacrolimus as Antifungal Agent.

Tacrolimus (FK506) is an immunosuppressant drug widely used to avoid organ rejection in transplant patients. It has a profound influence on the cellular stress response by interfering with the calmodulin-calcineurin signaling pathway. In this context FK506 also became a valuable antifungal drug in medical care. Here it is shown in vitro that tacrolimus has a potent growth inhibition activity against 11 fungi and 3 oomycetes of agricultural importance. The significance of this finding is discussed with respect to crop protection. The in silico molecular docking to 6 major antifungal enzymes determined UDP-N-acetylmuramoyl-L-alanine: D-glutamate ligase (MurD) as the main target by the best affinity score.

Novel acyl thiourea derivatives: Synthesis, antifungal activity, gene toxicity, drug-like and molecular docking screening.

Nine novel acyl thioureas were synthesized. Their identities and purities were confirmed by LC-MS spectra; each structure was elucidated by elemental analysis, IR, 1 Н and 13 C NMR spectra. Applying an in vitro screening of their antifungal potential, three substances (3, 5, and 6) could be selected as showing high activity against 11 fungi and 3 Phytophthora strains of phytopathogenic significance. Analysis of gene toxicity with the Salmonella reverse mutagenicity test, as an assessment of drug likeness, lipophilicity, and calculations of frontier molecular orbitals assign a low toxicity profile to these compounds. Molecular docking studies point to 14α-demethylase (CYP51) and N-myristoyltransferase (NMT) as possible fungal targets for growth inhibition. The findings are discussed with respect to structure-activity relationship (SAR).

Monomethyl Suberate Screening for Antifungal Activity, Molecular Docking and Drug-Like Properties.

Antifungal activity of suberic acid monomethyl ester (monomethyl suberate) was investigated in a growth inhibition assay comprising of 11 different fungi and 3 Phytophthora oomycetes strains relevant in agriculture. In comparison to standard antifungal hymexazol, monomethyl suberate showed moderate antifungal effects at a concentration range of 100-300 µg/mL. Alternaria alternata, Fusarium equiseti, Fusarium fujikuroi and Phytophtora infestans GL-1 were the most sensitive fungi showing inhibition rates up to 100 %. Physico-chemical descriptors of monomethyl suberate revealed its low toxicity profile. Molecular docking analysis comprising several known antifungal targets points to the N-myristoyltransferase as the most probable site of interaction.