Bioisosteric investigation of ebselen: Synthesis and in vitro characterization of 1,2-benzisothiazol-3(2H)-one derivatives as potent New Delhi metallo-ß-lactamase inhibitors.

Carbapenem-resistant Enterobacteriaceae (CRE) producing New Delhi metallo-ß-lactamase (NDM-1) cause untreatable bacterial infections, posing a significant threat to human health. In the present study, by employing the concept of bioisosteric replacement of the selenium moiety of ebselen, we have designed, synthesized and characterized a small compound library of 2-substituted 1,2-benzisothiazol-3(2H)-one derivatives and related compounds for evaluating their cytotoxicity and synergistic activity in combination with meropenem against the E. coli Tg1 (NDM-1) strain. The most promising compound 3a demonstrated potent synergistic activity against a panel of clinically isolated NDM-1 positive CRE strains with FICI as low as 0.09. Moreover, its IC50 value and inhibition mechanism were also confirmed by using the enzyme inhibition assay and the ESI-MS analysis respectively. Importantly, compound 3a has acceptable toxicity and is not a PAINS. Because of its structural simplicity and potent synergistic activity in combination with meropenem, we propose that compound 3a may be a promising meropenem adjuvant and a new series of such compounds may worth further investigations.

Boosting the efficacy of anti-MRSA ß-lactam antibiotics via an easily accessible, non-cytotoxic and orally bioavailable FtsZ inhibitor.

The rapid emergence of methicillin-resistant Staphylococcus aureus (MRSA) strains has undermined the therapeutic efficacy of existing ß-lactam antibiotics (BLAs), prompting an urgent need to discover novel BLAs adjuvants that can potentiate their anti-MRSA activities. In this study, cytotoxicity and antibacterial screening of a focused compound library enabled us to identify a compound, namely 28, which exhibited low cytotoxicity against normal cells and robust in vitro bactericidal synergy with different classes of BLAs against a panel of multidrug-resistant clinical MRSA isolates. A series of biochemical assays and microscopic studies have revealed that compound 28 is likely to interact with the S. aureus FtsZ protein at the T7-loop binding pocket and inhibit polymerization of FtsZ protein without interfering with its GTPase activity, resulting in extensive delocalization of Z-ring and morphological changes characterized by significant enlargement of the bacterial cell. Animal studies demonstrated that compound 28 had a favorable pharmacokinetic profile and exhibited potent synergistic efficacy with cefuroxime antibiotic in a murine systemic infection model of MRSA. Overall, compound 28 represents a promising lead of FtsZ inhibitor for further development of efficacious BLAs adjuvants to treat the staphylococcal infection.

Investigation of synergistic antimicrobial effects of the drug combinations of meropenem and 1,2-benzisoselenazol-3(2H)-one derivatives on carbapenem-resistant Enterobacteriaceae producing NDM-1.

The worldwide prevalence of NDM-1-producing bacteria has drastically undermined the clinical efficacy of the last line antibiotic of carbapenems, prompting a need to devise effective strategy to preserve their clinical value. Our previous studies have shown that ebselen can restore the efficacy of meropenem against a laboratory strain that produces NDM-1. Here we report the construction of a focused compound library of 1,2-benzisoselenazol-3(2H)-one derivatives which comprise a total of forty-six candidate compounds. The structure-activity relationship of these compounds and their potential to serve as an adjuvant to enhance the antimicrobial efficacy of meropenem against a collection of clinical NDM-1-producing carbapenem-resistant Enterobacteriaceae isolates was examined. Drug combination assays indicated that these derivatives exhibited synergistic antimicrobial activity when used along with meropenem, effectively restoring the activity of carbapenems against the resistant strains tested in a Galleria mellonella larvae in vivo infection model. The mode of inhibition of one compound, namely 11_a38, which was depicted when tested on the purified NDM-1 enzyme, indicated that it could covalently bind to the enzyme and displaced one zinc ion from the active site. Overall, this study provides a novel 1,2-benzisoselenazol-3(2H)-one scaffold that exhibits strong synergistic antimicrobial activity with carbapenems, and low cytotoxicity. The prospect of application of such compounds as carbapenem adjuvants warrants further evaluation.

Efficient synthesis and antioxidant activities of N-heterocyclyl substituted Coenzyme Q analogues.

A new strategy for the efficient synthesis of C-5 heterocyclyl substituted Coenzyme Q analogues was developed by N-alkylation of bromomethylated quinone 11 with a series of amines 12 under metal-free conditions. In vitro antioxidant activities of these Coenzyme Q analogues were evaluated and compared with commercial antioxidant Coenzyme Q10 by employing DPPH assay. All these N-heterocyclyl substituted Coenzyme Q analogues are found to be exhibiting good antioxidant properties and may be used as potent antioxidants for combating oxidative stress.

Transgenic Rice Expressing Ictb and FBP/Sbpase Derived from Cyanobacteria Exhibits Enhanced Photosynthesis and Mesophyll Conductance to CO2.

To find a way to promote the rate of carbon flux and further improve the photosynthetic rate in rice, two CO2-transporting and fixing relevant genes, Ictb and FBP/Sbpase, which were derived from cyanobacteria with the 35SCaMV promotor in the respective constructs, were transformed into rice. Three homologous transgenic groups with Ictb, FBP/Sbpase and the two genes combined were constructed in parallel, and the functional effects of these two genes were investigated by physiological, biochemical and leaf anatomy analyses. The results indicated that the mesophyll conductance and net photosynthetic rate were higher at approximately 10.5-36.8% and 13.5-34.6%, respectively, in the three groups but without any changes in leaf anatomy structure compared with wild type. Other physiological and biochemical parameters increased with the same trend in the three groups, which showed that the effect of FBP/SBPase on improving photosynthetic capacity was better than that of ICTB and that there was an additive effect in ICTB+FBP/SBPase. ICTB localized in the cytoplasm, whereas FBP/SBPase was successfully transported to the chloroplast. The two genes might show a synergistic interaction to promote carbon flow and the assimilation rate as a whole. The multigene transformation engineering and its potential utility for improving the photosynthetic capacity and yield in rice were discussed.

Modification of marine natural product ningalin B and SAR study lead to potent P-glycoprotein inhibitors.

In this study, new marine ningalin B analogues containing a piperazine or a benzoloxy group at ring C have been synthesized and evaluated on their P-gp modulating activity in human breast cancer and leukemia cell lines. Their structure-activity relationship was preliminarily studied. Compounds 19 and 20 are potent P-gp inhibitors. These two synthetic analogues of permethyl ningalin B may be potentially used as effective modulators of P-gp-mediated drug resistance in cancer cells.