Search

The increasing prevalence of metallo‐β‐lactamase (MBL)‐expressing bacteria presents a worrying trend in antibiotic resistance. MBLs rely on active site zinc ions for their hydrolytic activity and the pursuit of MBL‐inhibitors has therefore involved the investigation of zinc chelators. To ensure that such chelators specifically target MBLs, a series of cephalosporin prodrugs of two potent zinc‐binders: dipicolinic acid (DPA) and 8‐thioquinoline (8‐TQ) was prepared. Although both DPA and 8‐TQ bind free zinc very tightly (K d values in the low nm range), the corresponding cephalosporin conjugates do not. The cephalosporin conjugates are efficiently hydrolyzed by MBLs to release DPA or 8‐TQ, as confirmed by using both NMR and LC‐MS studies. Notably, the cephalosporin prodrugs of DPA and 8‐TQ show potent inhibitory activity against NDM, VIM, and IMP classes of MBLs and display potent synergy with meropenem against MBL‐expressing clinical isolates of K. pneumoniae and E. coli., Stopping bacterial resistance: Metallo‐β‐lactamases (MBLs) are bacterial resistance enzymes that degrade β‐lactam antibiotics, including last line of defense carbapenems like meropenem. A new series of cephalosporin prodrug inhibitors that exploit the hydrolytic action of the target MBL itself to activate the inhibitor is reported. The prodrugs display potent MBL inhibition and effectively synergize with meropenem against highly resistant MBL‐expressing isolates.

Brevicidine and laterocidine are two recently discovered lipopeptide antibiotics with promising antibacterial activity. Possessing a macrocyclic core, multiple positive charges, and a lipidated N-terminus, these lipopeptides exhibit potent and selective activity against Gram-negative pathogens, including polymyxin-resistant isolates. Given the low amounts of brevicidine and laterocidine accessible by fermentation of the producing microorganisms, synthetic routes to these lipopeptides present an attractive alternative. We here report the convenient solid-phase syntheses of both brevicidine and laterocidine and confirm their potent anti-Gram-negative activities. The synthetic routes developed also provide convenient access to novel structural analogues of both brevicidine and laterocidine that display improved hydrolytic stability while maintaining potent antibacterial activity in both in vitro assays and in vivo infection models.

Brevicidine and laterocidine are two recently discovered lipopeptide antibiotics with promising antibacterial activity. Possessing a macrocyclic core, multiple positive charges, and a lipidated N-terminus, these lipopeptides exhibit potent and selective activity against Gram-negative pathogens, including polymyxin-resistant isolates. Given the low amounts of brevicidine and laterocidine accessible by fermentation of the producing microorganisms, synthetic routes to these lipopeptides present an attractive alternative. We here report the convenient solid-phase syntheses of both brevicidine and laterocidine and confirm their potent anti-Gram-negative activities. The synthetic routes developed also provide convenient access to novel structural analogues of both brevicidine and laterocidine that display improved hydrolytic stability while maintaining potent antibacterial activity in both

Metallo‐β‐lactamases (MBLs) are zinc‐dependent bacterial enzymes that inactivate essentially all classes of β‐lactam antibiotics including last‐resort carbapenems. At present there are no clinically approved MBL inhibitors, and in order to develop such agents it is essential to understand their inhibitory mechanisms. Herein, we describe a comprehensive mechanistic study of a panel of structurally distinct MBL inhibitors reported in both the scientific and patent literature. Specifically, we determined the half‐maximal inhibitory concentration (IC50) for each inhibitor against MBLs belonging to the NDM and IMP families. In addition, the binding affinities of the inhibitors for Zn2+, Ca2+ and Mg2+ were assessed by using isothermal titration calorimetry (ITC). We also compared the ability of the different inhibitors to resensitize a highly resistant MBL‐expressing Escherichia coli strain to meropenem. These investigations reveal clear differences between the MBL inhibitors studied in terms of their IC50 value, metal binding ability, and capacity to synergize with meropenem. Notably, our studies demonstrate that potent MBL inhibition and synergy with meropenem are not explicitly dependent on the capacity of an inhibitor to strongly chelate zinc., Developing broad‐spectrum MBL inhibitors: Structurally diverse MBL inhibitors were assessed for their ability to inhibit purified MBL enzymes, bind various divalent cations, and resensitize a carbapenem‐resistant E. coli strain to meropenem. These studies reveal that potent MBL inhibition and synergy with meropenem is not explicitly dependent on the ability of an inhibitor to bind free zinc with high affinity.

In an attempt to exploit the hydrolytic mechanism by which β-lactamases degrade cephalosporins, we designed and synthesized a series of novel cephalosporin prodrugs aimed at delivering thiol-based inhibitors of metallo-β-lactamases (MBLs) in a spatiotemporally controlled fashion. While enzymatic hydrolysis of the β-lactam ring was observed, it was not accompanied by inhibitor release. Nonetheless, the cephalosporin prodrugs, especially thiomandelic acid conjugate (8), demonstrated potent inhibition of IMP-type MBLs. In addition, conjugate 8 was also found to greatly reduce the minimum inhibitory concentration of meropenem against IMP-producing bacteria. The results of kinetic experiments indicate that these prodrugs inhibit IMP-type MBLs by acting as slowly turned-over substrates. Structure–activity relationship studies revealed that both phenyl and carboxyl moieties of 8 are crucial for its potency. Furthermore, modeling studies indicate that productive interactions of the thiomandelic acid moiety of 8 with Trp28 within the IMP active site may contribute to its potency and selectivity.

Polysialic acid (polySia) are α2,8- and/or α2,9-linked homopolymers with interesting properties for meningococcal vaccine development or the cure of human neurodegenerative disorders. With the goal to avoid large scale production of pathogenic bacteria, we compare in the current study the efficacy of conventional polySia production to recombinant approaches using the engineered laboratory safety strain E. coli BL21. High cell density cultivation (HCDC) experiments were performed in two different bioreactor systems. Increased cell densities of up to 11.3 (±0.4) g/L and polySia concentrations of up to 774 (±18) mg/L were reached in E. coli K1. However, cultivation of engineered E. coli BL21 strains delivered comparable cell densities but a maximum of only 133 mg/L polySia. Using established downstream procedures, host cell DNA and proteins were removed. All recombinant polySia products showed an identical degree of polymerization >90. Polymers with different glycosidic linkages could be successfully differentiated by nuclear magnetic resonance spectroscopy.

In the search for new inhibitors of bacterial metallo-β-lactamases (MBLs), a series of commonly used small molecule carboxylic acid derivatives were evaluated for their ability to inhibit New Delhi metallo-β-lactamase (NDM)-, Verona integron-encoded metallo-β-lactamase (VIM)-, and imipenemase (IMP)-type enzymes. Nitrilotriacetic acid (3) and N-(phosphonomethyl)iminodiacetic acid (5) showed promising activity especially against NDM-1 and VIM-2 with IC50 values in the low-to-sub μM range. Binding assays using isothermal titration calorimetry reveal that 3 and 5 bind zinc with high affinity with dissociation constant (Kd) values of 121 and 56 nM, respectively. The in vitro biological activity of 3 and 5 against E. coli expressing NDM-1 was evaluated in checkerboard format, demonstrating a strong synergistic relationship for both compounds when combined with Meropenem. Compounds 3 and 5 were then tested against 35 pathogenic strains expressing MBLs of the NDM, VIM, or IMP classes. Notably, when combined with Meropenem, compounds 3 and 5 were found to lower the minimum inhibitory concentration (MIC) of Meropenem up to 128-fold against strains producing NDM- and VIM-type enzymes.

A series of aminocarboxylic acid analogues of aspergillomarasmine A (AMA) and ethylenediamine-N,N'-disuccinic acid (EDDS) were chemoenzymatically synthesized via the addition of various mono- and diamine substrates to fumaric acid catalyzed by the enzyme EDDS lyase. Many of these novel AMA and EDDS analogues demonstrate potent inhibition of the bacterial metallo-β-lactamase NDM-1. Isothermal titration calorimetry assays revealed a strong correlation between the inhibitory potency of the compounds and their ability to bind zinc. Compounds 1a (AMA), 1b (AMB), 5 (EDDS), followed by 1d and 8a, demonstrate the highest synergy with meropenem resensitizing an NDM-1 producing strain of E. coli to this important carbapenem of last resort.