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Readily available, naturally derived lignin was transformed into a Brønsted acidic organocatalyst. The obtained catalyst was utilized in the environmentally benign synthesis of biologically relevant indole derivatives such as vibrindole, turbomycin, etc. The scope of the developed methodology was further extended for the synthesis of aniline-tethered indoles, 4H-chromene, and indolin-2-one derivatives. Further, vicinal difunctionalization was successfully carried out with the aid of the developed organocatalyst. Imperatively, all the aforementioned reactions were carried out in the aqueous medium. The reusability of the heterogeneous catalyst was also proved by carrying out the reaction with the recovered catalyst. Lignin-based naturally derived Brønsted acidic organocatalyst was utilized in the environmentally benign synthesis of biologically relevant indole derivatives, 4H-chromene, and indolin-2-one derivatives. All the aforementioned transformations were carried out in an environmentally benign aqueous medium. [ABSTRACT FROM AUTHOR]

The domestic and industrial utilization of cotton fiber is largely restricted primarily due to its highly flammable nature. Although halogen-based molecules impart appreciable flame retardancy to cotton, they have notable disadvantages. This review offers comprehensive coverage of naturally derived flame-retardant molecules as an effective alternative to halogen-based flame-retardants. The source of each type of naturally derived flame-retardants, their structural significance, advantages, and role of additives in enhancing the flame-retardant properties were discussed in detail. Apart from highlighting the significance of lignin, deoxyribonucleic acid (DNA), phytic acid, casein, etc., this review article also discusses flame-retardants derived from chicken feathers, egg shells, and hydrophobins. In addition, this review highlights the limitations associated with the naturally derived flame-retardants and provides future perspectives. [ABSTRACT FROM AUTHOR]

A series of tetrahydroquinoline derivatives were synthesized in good yields through Cu(OAc)2/t-butyl hydroperoxide (TBHP) assisted oxidative cyclization reaction. All the reactions were carried out in the aqueous medium at room temperature itself. In the oxidative cyclization reaction, dual functionalization of C(sp3)-H and C(sp2)-H bonds of the N,N-dimethylaniline was achieved in one-pot operation under mild reaction conditions. TBHP assisted synthesis of tetrahydroquinoline analogues was also successfully performed in the aqueous KCl medium in the absence of copper catalyst. [ABSTRACT FROM AUTHOR]

Antibiotics like colistin are the last resort to deal with infections by carbapenem-resistant Enterobacteriaceae (CREB). Resistance to colistin severely restricts therapeutic options. To tackle this dire situation, urgent measures to restore colistin sensitivity are needed. In this study, whole-genome sequencing of colistin-resistant E. coli strain was performed and the genome analysis revealed that the strain belonged to the sequence type ST405. Multiple mutations were observed in genes implicated in colistin resistance, especially those related to the L-Ara-4-N pathway but mgrB was unmutated and mcr1-9 genes were missing. MarR inhibitor salicylate was used to re-sensitize this strain to colistin, which increased the negative charge on the cell surface especially in colistin resistant E. coli (U3790 strain) and thereby facilitated a decrease in colistin MIC by 8 fold. It is indeed well known that MarR inhibition by salicylate triggers the expression of AcrAB efflux pumps through MarA. So, in order to fully restore colistin sensitivity, a potent efflux pump inhibitor (BC1), identified earlier by this group was employed. The combination of colistin with both salicylate and BC1 caused a remarkable 6 log reduction in cell counts of U3790 in time-kill assay. Infection of muscle tissue of zebrafish with U3790 followed by various treatments showed that the combination of colistin + salicylate + BC1 was highly effective in reducing bioburden in infected muscle tissue by 4 log fold. Thus, our study shows that a combination of MarR inhibitor to enhance colistin binding and efflux pump inhibitor to reduce colistin extrusion was highly effective in restoring colistin sensitivity in colistin-resistant clinical isolate of E. coli in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Colistin resistance in Enterobacteriaceae especially Klebsiella pneumoniae and Escherichia coli is driving the evolution of pan drug resistant strains. Screening a library of 13 plant nutraceuticals led to the identification of acetyl shikonin and ursolic acid, which exhibited synergy with colistin against extremely drug resistant (XDR) clinical strains of E. coli (U3790) and K. pneumoniae (BC936). Ursolic acid caused a significant colistin MIC reversal of 16-fold in U3790 and 4-fold in BC936 strains. Ursolic acid also potentiated the bactericidal effect of colistin against both U3790 and BC936 by causing ~ 4 to 4.5 log fold decline in CFU of both clinical isolates in a time kill assay. At 2× minimum effective concentration, ursolic acid was non-toxic to zebrafish as evidenced by brain and liver enzyme profiles and by histopathology studies. In combination with colistin, ursolic acid reduced bacterial bioburden of U3790/BC936 by 1-1.58 log fold from the infected muscle tissue of zebrafish. Mechanistic explorations via studies on real time efflux, membrane potential and intracellular accumulation of dansyl chloride tagged colistin revealed that colistin efflux is inhibited by ursolic acid. In addition, ursolic acid also enhanced outer membrane permeability which probably facilitates colistin's attack on outer and inner membranes. Our study shows that ursolic acid synergizes with colistin by inhibiting colistin efflux in Enterobacteriaceae that helps to curtail colistin resistant Enterobacteriaceae. [ABSTRACT FROM AUTHOR]