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Aspergillus montevidensis is an important domesticated fungus that has been applied to produce many traditional fermented foods under high osmotic conditions. However, the detailed mechanisms of tolerance to osmotic stress remain largely unknown. Here, we construct a target-deleted strain (ΔLeuRS) of A. montevidensis and found that the ΔLeuRS mutants grew slowly and suppressed the development of the cleistothecium compared to the wide-type strains (WT) under salt-stressed and non-stressed conditions. Furthermore, differentially expressed genes (p < 0.001) governed by LeuRS were involved in salt tolerance, ABC transporter, amino acid metabolism, sugar metabolism, and the reproduction process. The ΔLeuRS strains compared to WT strains under short- and long-term salinity stress especially altered accumulation levels of metabolites, such as amino acids and derivatives, carbohydrates, organic acids, and fatty acids. This study provides new insights into the underlying mechanisms of salinity tolerance and lays a foundation for flavor improvement of foods fermented with A. montevidensis.

The current study is focused on the combination of pyrazinamide with 6-aminobenzo[c][1,2]oxaborol-1(3H)-ol, which is a crucial pharmacophore of several antimicrobial agents. The use of benzoxaborole moiety could afford the formation of a spiro adduct between benzoxaborole moiety and 3'-terminal adenosine nucleotide Ade76 of tRNALeu. In the form of this spiro adduct, it may potentially inhibit the enzyme leucyl-tRNA synthetase (LeuRS). A large heterocyclic substitution in position 6 of the benzoxaborole moiety could lead to the enhanced selectivity of the intended compounds to the bacterial enzyme due to steric clashes with eukaryotic types of LeuRS. The target compounds were synthesized by condensation of 6-aminobenzo[c][1,2]oxaborol-1(3H)-ol with variously substituted heteroaromatic acids that underwent previous activation. The synthetic products and the isolated condensation intermediates were subjected to biological in vitro screening against fungi and bacteria, including mycobacteria and in vitro cytotoxicity screening against the HepG2 cancer cell line. Some of the compounds showed moderate antimycobacterial activity with persisted low toxicity.

A series of novel 7-oxo-7H-thiazolo[3,2-b]-1,2,4-triazine-2-carboxylic acid derivatives was synthesized in good yields by a multi-step procedure that included the generation of the S-alkylated derivatives from 6-substituted arylmethyl-3-mercapto-1,2,4-triazin-5-ones with ethyl 2-chloroacetoacetate, intramolecular cyclization with microwave irradiation, hydrolysis and amidation. All of the target compounds were fully characterized through 1H-NMR, 13C-NMR and HRMS spectra. The intramolecular cyclization occurred regioselectively at the N2-position of 1,2,4-triazine ring, which was confirmed by compound 3e using single-crystal X-ray diffraction analysis. The antibacterial and antitubercular activities of the target compounds were evaluated. Compared with Ciprofloxacin and Rifampicin, compounds 5d, 5f and 5g containing the terminal amide fragment exhibited broad spectrum antibacterial activity, and carboxylic acid derivatives or its corresponding ethyl esters had less effect on antibacterial properties. The most potent compound 5f also displayed excellent in vitro antitubercular activity against Mycobacterium smegmatis (minimum inhibitory concentration (MIC) = 50 μg/mL) and better growth inhibition activity of leucyl-tRNA synthetase (78.24 ± 4.05% at 15 μg/mL).