Activity of Imipenem, Meropenem, Cefepime, and Sulbactam in Combination with the ß-Lactamase Inhibitor LN-1-255 against Acinetobacter spp.

Treatment of infections caused by Acinetobacter spp., particularly A. baumannii, is a major clinical problem due to its high rates of antibiotic resistance. New strategies must be developed; therefore, restoration of ß-lactam efficacy through the use of ß-lactamase inhibitors is paramount. Activities of the antibiotics imipenem, meropenem, cefepime, and sulbactam in combination with the penicillin-sulfone inhibitor LN-1-255 were tested by microdilution against 148 isolates of Acinetobacter spp. collected in 14 hospitals in Spain in 2020. Relevantly, the MIC90 (i.e., minimum concentration at which 90% of isolates were inhibited) of antibiotics in combination with LN-1-255 decreased 4- to 8-fold for all of the Acinetobacter isolates. Considering only the carbapenem-resistant A. baumannii isolates, which produce carbapenem-hydrolyzing class D ß-lactamases, the addition of LN-1-255 decreased the resistance rates from 95.1% to 0% for imipenem, from 100% to 9.8% for meropenem, from 70.7% to 7.3% for cefepime, and sulbactam resistance rates from 9.8% to 0% and intermediate susceptibility rates from 53.7% to 2.4%. The inhibitor also decreased the minimum inhibitory concentrations (MICs) when tested against non-carbapenem-resistant Acinetobacter spp. isolates. In conclusion, combining LN-1-255 with imipenem, meropenem, cefepime, and sulbactam to target A. baumannii, and especially carbapenem-resistant isolates, represents an attractive option that should be developed for the treatment of infections caused by this pathogen.

Axially chiral triazoloisoquinolin-3-ylidene ligands in gold(I)-catalyzed asymmetric intermolecular (4 + 2) cycloadditions of allenamides and dienes.

The first highly enantioselective intermolecular (4 + 2) cycloaddition between allenes and dienes is reported. The reaction provides good yields of optically active cyclohexenes featuring diverse substitution patterns and up to three stereocenters. Key to the success of the process is the use of newly designed axially chiral N-heterocyclic carbene-gold catalysts.

Theoretical study on intramolecular allene-diene cycloadditions catalyzed by PtCl2 and Au(I) complexes.

The intramolecular [4C+3C] cycloaddition reaction of allenedienes catalysed by PtCl(2) and several Au(I) complexes has been studied by means of DFT calculations. Overall, the reaction mechanism comprises three main steps: (i) the formation of a metal allyl cation intermediate, (ii) a [4C(4π)+3C(2π)] cycloaddition that produces a seven-membered ring and (iii) a 1,2-hydrogen migration process on these intermediates. The reaction proceeds with complete diastereochemical control resulting from a favoured exo-like cycloaddition. Allene substituents have a critical influence in the reaction outcome and mechanism. The experimental observation of [4C+2C] cycloadducts in the reaction of substrates lacking substituents at the allene terminus can be explained through a mechanism involving Pt(IV)-metallacycles. With gold catalysts it is also possible to obtain [4C+2C] cycloaddition products, but only with substrates featuring terminally disubstituted allenes, and employing π-acceptor ligands at gold. However the mechanism for the formation of these adducts is completely different to that proposed with PtCl(2), and consists of the formation of a metal allyl cation, subsequent [4C+3C] cycloaddition and a 1,2-alkyl shift (ring contraction). Electronic analysis indicates that the divergent pathways are mainly controlled by the electronic properties of the gold heptacyclic species (L-Au-C(2)), in particular, the backdonation capacity of the metal center to the unoccupied C(2) (pπ-orbital) of the intermediate resulting from the [4C+3C] cycloaddition. The less backdonation, (i.e. using P(OR)(3)Au(+) complexes), the more favoured is the 1,2-alkyl shift.

Gold-catalyzed [4C+2C] cycloadditions of allenedienes, including an enantioselective version with new phosphoramidite-based catalysts: mechanistic aspects of the divergence between [4C+3C] and [4C+2C] pathways.

Gold(I) complexes featuring electron acceptor ligands such as phosphites and phosphoramidites catalyze the [4C+2C] intramolecular cycloaddition of allenedienes. The reaction is chemo- and stereoselective, and provides trans-fused bicyclic cycloadducts in good yields. Moreover, using novel chiral phosphoramidite-based gold catalysts it is possible to perform the reaction with excellent enantioselectivity. Experimental and theoretical data dismiss a cationic mechanism involving intermediate II and suggest that the formation of the [4C+2C] cycloadducts might arise from a 1,2-alkyl migration (ring contraction) in a cycloheptenyl Au-carbene intermediate (IV), itself arising from a [4C+3C] concerted cycloaddition of the allenediene. Therefore, these [4C+2C] allenediene cycloadditions and the previously reported [4C+3C] counterparts most likely share such cycloaddition step, differing in the final 1,2-migration step.