A new procedure for thioester deprotection using thioglycolic acid in both homogeneous and heterogeneous phase

Stereoselective Synthesis of 1,2-cis-α-Glycosyl Thiols and Trehalose-Type α,α'-Thiodisaccharides by Cryo Thiol-Ene Photocoupling - Thio-Click Reaction in Frozen State

α-Glycosyl thiols are key building blocks for the formation of stable thioglycoside mimetics of widespread and biologically relevant α-O-glycosides, which urges their efficient synthesis. Here, we demonstrate that the photoinitiated radical-mediated addition of thioacetic acid to 2-substituted glycals followed by selective S-deacetylation is a generally applicable and fully stereoselective method for the synthesis of 1,2-cis-α-glycosyl thiols. The low reactivity of thioacetic acid in the radical reaction was overcome by carrying out the reaction in AcOH at -80 °C, in frozen state, with UVA irradiation, achieving high yields irrespective of the sugar configurations. For effective irradiation and simultaneous effective cooling, a self-made spiral vessel reactor was used, which also enables large-scale synthesis. By subjecting 1,2-cis-α-1-thiosugars to a second thiol-ene coupling reaction with 2-substituted glycals, 34 trehalose-type symmetrical and unsymmetrical α,α'-thiodi- and oligosaccharides were obtained with full stereoselectivity. Moreover, the oxidation of α-1-thiosugars provided an easy access to α,α'-diglycosyl disulfides.

Impact of tebipenem pivoxil on the intestinal microbiota and on establishment of colonization with carbapenem-resistant Klebsiella pneumoniae in mice

Tebipenem pivoxil has potent in vitro activity against Enterobacterales pathogens, but requires combination with β-lactamase inhibitor to achieve activity against carbapenemase producers, including metallo-β-lactamases (MBLs). Herein, we evaluate the potential of tebipenem pivoxil, alone and in combination with the prodrug of the experimental MBL inhibitor CS319 (CS319-piv-SAc), to disrupt the indigenous mice microbiota of the colon and promote colonization by pathogens. The effect of antibiotic treatment (daily for 3 days with subcutaneous saline [control], subcutaneous clindamycin, oral tebipenem pivoxil alone and in combination with CS319-piv-Sac, or oral CS319-piv-Sac) on the intestinal microbiota was assessed by culture for enterococci and facultative Gram-negative bacilli and by 16S rRNA amplicon sequencing. Mice were also challenged with 10,000 colony-forming units (CFU) of multidrug-resistant (MDR) strain Klebsiella pneumoniae blaNDM-1, 6 h after the second dose. The concentrations of the MDR K. pneumoniae in stool were measured on days 1, 3, and 6 after challenge. In comparison to saline controls, clindamycin (P = 0.001) and tebipenem pivoxil plus CS319-piv-SAc (P = 0.02) treatment resulted in significant changes in the alpha diversity patterns, whereas tebipenem pivoxil and CS319-piv-SAc individual treatments did not (P > 0.05). Moreover, clindamycin treatment resulted in substantial overgrowth of MDR K. pneumoniae (mean concentration after 6 days of infection, 6.1 vs 2.9 log10 CFU/g stool), whereas the other treatments did not (≤3.6 log10 CFU/g). Although tebipenem pivoxil alone or in combination with an MBL inhibitor, CS319, caused alteration of the mice intestinal microbiota, neither treatment promoted overgrowth of carbapenem-resistant K. pneumoniae.IMPORTANCEIn this work, we used a mouse model to determine the impact of tebipenem pivoxil alone and in combination with a prodrug of an experimental metallo-β-lactamase inhibitor, CS319, on the intestinal microbiota and on the establishment of colonization with carbapenem-resistant Klebsiella pneumoniae. We found that while treatment with tebipenem pivoxil plus the prodrug of CS319 caused alteration of the intestinal microbiota, it did not promote the overgrowth of carbapenem-resistant K. pneumoniae. Although additional studies are needed to examine the impact of tebipenem pivoxil treatment on other multidrug-resistant Gram-negative bacilli, Clostridioides difficile, and Candida spp., our study is a step forward in the understanding of the potential effect of this oral carbapenem on the indigenous microbiota of the colon and on the promotion of colonization by pathogens.

Thioester deprotection using a biomimetic NCL approach

The reversibility of the thiol-thioester linkage has been broadly employed in many fields of biochemistry (lipid synthesis) and chemistry (dynamic combinatorial chemistry and material science). When the transthioesterification is followed by a S-to-N acyl transfer to give an amide bond, it is called Native Chemical Ligation (NCL), a high-yield chemoselective process used for peptide synthesis. Recently, we described thioglycolic acid (TGA) as a useful reagent for thioester deprotection both in solution and anchored to a solid-support under mild conditions. Inspired by NCL, in this work, we extended this approach and explored the use of 2-aminothiols for the deprotection of thiols bearing an acyl group. The best results were obtained using cysteamine or L-cysteine in an aqueous buffer pH 8 at room temperature for 30 min. The described approach was useful for S-acetyl, S-butyryl, and S-benzoyl heterocycles deprotection with yields up to 84%. Employing this methodology, we prepared six new analogs 2 of mercaptomethyl bisthiazolidine 1, a useful inhibitor of a wide-range of Metallo-β-Lactamases (MBLs). Compared with the previous methodologies (TGA polymer supported and TGA in solution), the biomimetic deprotection herein described presents better performance with higher yields, shorter reaction times, less time-consuming operations, easier setup, and lower costs.