GaMF1.39's antibiotic efficacy and its enhanced antitubercular activity in combination with clofazimine, Telacebec, ND-011992, or TBAJ-876

IMPORTANCE

New drugs are needed to combat multidrug-resistant tuberculosis. The electron transport chain (ETC) maintains the electrochemical potential across the cytoplasmic membrane and allows the production of ATP, the energy currency of any living cell. The mycobacterial engine F-ATP synthase catalyzes the formation of ATP and has come into focus as an attractive and rich drug target. Recent deep insights into these mycobacterial F1FO-ATP synthase elements opened the door for a renaissance of structure-based target identification and inhibitor design. In this study, we present the GaMF1.39 antimycobacterial compound, targeting the rotary subunit γ of the biological engine. The compound is bactericidal, inhibits infection ex vivo, and displays enhanced anti-tuberculosis activity in combination with ETC inhibitors, which promises new strategies to shorten tuberculosis chemotherapy.

Synthesis and antimalarial activity of amide and ester conjugates of siderophores and ozonides

Despite advances in chemotherapeutic interventions for the treatment of malaria, there is a continuing need for the development of new antimalarial agents. Previous studies indicated that co-administration of chloroquine with antioxidants such as the iron chelator deferoxamine (DFO) prevented the development of persistent cognitive damage in surrogate models of cerebral malaria. The work described herein reports the syntheses and antimalarial activities of covalent conjugates of both natural (siderophores) and artificial iron chelators, namely DFO, ferricrocin and ICL-670, with antimalarial 1,2,4-trioxolanes (ozonides). All of the synthesized conjugates had potent antimalarial activities against the in vitro cultures of drug resistant and drug sensitive strains of Plasmodium falciparum. The work described herein provides the basis for future development of covalent combination of iron chelators and antimalarial chemotherapeutic agents for the treatment of cerebral malaria.

Brain Tissue Oxygen and BOLD fMRI Under Different Levels of Neuronal Activity

Localized increases in neuronal activity are supported by the hemodynamic response, which delivers oxygen to the brain tissue to support synaptic functions, action potentials and other neuronal processes. However, it remains unknown if changes in baseline neuronal activity, which are expected to reflect neuronal metabolic demand, alter the relationship between the local hemodynamic and oxygen behaviour. In order to better characterize this system, we examine here the relationship between brain tissue oxygen (PO2) and hemodynamic responses (BOLD functional MRI) under different levels of neuronal activity. By comparing the stimulus-evoked responses during different levels of baseline neuronal activity, the awake state vs isoflurane anesthesia, we were able to measure how a known change in neuronal demand affected tissue PO2 as well as the hemodynamic response to stimulation. We observed a high correlation between stimulus-evoked PO2 and BOLD responses in the awake state. Moreover, we found that the evoked PO2 and BOLD responses were still present despite the elevated tissue oxygen baseline and decreased baseline of neuronal activity under low concentration isoflurane, and that the magnitudes of these responses decreased by similar proportions but the relationship between these signals was distorted. Our findings point to distortion of the BOLD-PO2 relationship due to anesthesia. The feedback mechanism to adjust the level of brain tissue oxygen, as well as the correlation between BOLD and PO2 responses, are impaired even by a small dose of anesthetics.

Conjugation of Aztreonam, a Synthetic Monocyclic β-Lactam Antibiotic, to a Siderophore Mimetic Significantly Expands Activity Against Gram-Negative Bacteria

Monocyclic β-lactams with antibiotic activity were first synthesized more than 40 years ago. Extensive early structure-activity relationship (SAR) studies, especially in the 1980s, emphasized the need for heteroatom activation of monocyclic β-lactams and led to studies of oxamazins, monobactams, monosulfactams, and monocarbams with various side chains and peripheral substitution that revealed potent activity against select strains of Gram-negative bacteria. Aztreonam, still the only clinically used monobactam, has notable activity against many Gram-negative bacteria but limited activity against some of the most problematic multidrug resistant (MDR) strains of Pseudomonas aeruginosa and Acinetobacter baumannii. Herein, we report that extension of the side chain of aztreonam is tolerated and especially that coupling of the side chain free acid with a bis-catechol siderophore mimetic significantly improves activity against the MDR strains of Gram-negative bacteria that are of most significant concern.

Design and Syntheses of New Antibiotics Inspired by Nature's Quest for Iron in an Oxidative Climate

This Account describes fundamental chemistry that promoted the discovery of new antibiotics. Specifically, the NH acidity of simple hydroxamic acid derivatives facilitated the syntheses of novel β-lactams (oxamazins and monobactams), siderophore mimics that limit bacterial iron uptake and bacterially targeted sideromycins (siderophore-antibiotic conjugates). The development of resistance to our current limited set of antibiotic scaffolds has created a dire medical situation. As recently stated, "if you weren't taking antibiotic resistance seriously before, now would be a good time to start." A project commissioned by the British government (https://amr-review.org/) has released estimates of the near-future global toll of antibiotic resistance that are jaw-dropping in their seriousness and scale: 10 million deaths per year and at least $100 trillion in sacrificed gross national product. The 2020 COVID pandemic confirmed that infectious disease problems are no longer localized but worldwide. Many classical antibiotics, especially β-lactams, previously provided economical cures, but the evolution of antibiotic destructive enzymes (i.e., β-lactamases), efflux pumps, and bacterial cell wall permeability barriers has made many types of bacteria, especially Gram-negative strains, resistant. Still, and in contrast to other therapies, the public expectation is that any new antibiotic must be inexpensive. This creates market limitations that have caused most major pharmaceutical companies to abandon antibiotic research. Much needs to be done to address this significant problem.The critical need for bacteria to sequester essential iron provides an Achilles' heel for new antibiotic development. Although ferric iron is extremely insoluble, bacteria need micromolar intracellular concentrations for growth and virulence. To this end, they biosynthesize siderophores (Gr. iron bearer) and excrete them into their environment, where they bind iron with high affinity. The iron complexes are recognized by specific outer-membrane transporters, and once actively internalized, the iron is released for essential processes. To conserve biosynthetic energy, some bacteria recognize and utilize siderophores made by competing strains. As a counter-revolution in the never-ending fight for survival, bacteria have also evolved sideromycins, which are siderophores conjugated to warheads that are lethal to rogue bacteria. While none are now used therapeutically, natural sideromycins called albomycins have been used clinically, and others have been shown to be well tolerated and active in animal infection models. Herein we describe practical methods to synthesize new antibiotics and artificial sideromycins with the generalized structure shown above (siderophore-linker drug). Utilizing the molecular-recognition-based siderophore/sideromycin bacterial assimilation processes, it is possible to design both broad spectrum and exquisitely narrow spectrum (targeted) sideromycins and even repurpose older or more classical antibiotics. Relevant microbiological assays, in vivo animal infection studies, and the recent FDA approval of cefiderocol demonstrate their effectiveness.

Dual inhibition of the terminal oxidases eradicates antibiotic-tolerant Mycobacterium tuberculosis

The approval of bedaquiline has placed energy metabolism in the limelight as an attractive target space for tuberculosis antibiotic development. While bedaquiline inhibits the mycobacterial F1 F0 ATP synthase, small molecules targeting other components of the oxidative phosphorylation pathway have been identified. Of particular interest is Telacebec (Q203), a phase 2 drug candidate inhibitor of the cytochrome bcc:aa3 terminal oxidase. A functional redundancy between the cytochrome bcc:aa3 and the cytochrome bd oxidase protects M. tuberculosis from Q203-induced death, highlighting the attractiveness of the bd-type terminal oxidase for drug development. Here, we employed a facile whole-cell screen approach to identify the cytochrome bd inhibitor ND-011992. Although ND-011992 is ineffective on its own, it inhibits respiration and ATP homeostasis in combination with Q203. The drug combination was bactericidal against replicating and antibiotic-tolerant, non-replicating mycobacteria, and increased efficacy relative to that of a single drug in a mouse model. These findings suggest that a cytochrome bd oxidase inhibitor will add value to a drug combination targeting oxidative phosphorylation for tuberculosis treatment.

Structure guided generation of thieno[3,2-d]pyrimidin-4-amine Mycobacterium tuberculosis bd oxidase inhibitors

Cytochrome bd oxidase (Cyt-bd) is an attractive drug target in Mycobacterium tuberculosis, especially in the context of developing a drug combination targeting energy metabolism. However, currently few synthetically assessable scaffolds target Cyt-bd. Herein, we report that thieno[3,2-d]pyrimidin-4-amines inhibit Cyt-bd, and report an initial structure-activity-relationship (SAR) of 13 compounds in three mycobacterial strains: Mycobacterium bovis BCG, Mycobacterium tuberculosis H37Rv and Mycobacterium tuberculosis clinical isolate N0145 in an established ATP depletion assay with or without the cytochrome bcc : aa 3 (QcrB) inhibitor Q203. All compounds displayed activity against M. bovis BCG and the M. tuberculosis clinical isolate strain N0145 with ATP IC50 values from 6 to 54 μM in the presence of Q203 only, as expected from a Cyt-bd inhibitor. All derivatives were much less potent against M. tuberculosis H37Rv compared to N0145 (IC50's from 24 to >100 μM and 9-52 μM, respectively), an observation that may be attributed to the higher expression of the Cyt-bd-encoding genes in the laboratory-adapted M. tuberculosis H37Rv strain. N-(4-(tert-butyl)phenethyl)thieno[3,2-d]pyrimidin-4-amine (19) was the most active compound with ATP IC50 values from 6 to 18 μM against all strains in the presence of Q203, making it a good chemical probe for interrogation the function of the mycobacterial Cyt-bd under various physiological conditions.

Hydride-induced Meisenheimer complex formation reflects activity of nitro aromatic anti-tuberculosis compounds

The formation efficiency of hydride-induced Meisenheimer complexes of nitroaromatic compounds is consistent with their anti-TB activities exemplied by MDL860 and benzothiazol N-oxide (BTO) analogs. Herein we report that nitro cyano phenoxybenzenes (MDL860 and analogs) reacted slowly and incompletely which reflected their moderate anti-TB activity, in contrast to the instantaneous reaction of BTO derivatives to quantitatively generate Meisenheimer complexes which corresponded to their enhanced anti-TB activity. These results were corroborated by mycobacterial and radiolabelling studies that confirmed inhibition of the DprE1 enzyme by BTO derivatives but not MDL860 analogs.

Crystallographic evidence for unintended benzisothiazolinone 1-oxide formation from benzothiazinones through oxidation

X-ray crystallography revealed the unintended formation of benziso­thia­zolinone 1-oxides from 1,3-benzo­thia­zin-4-ones through oxidation instead of the anti­cipated benzo­thia­zinone sulfones, which would be constitutional isomers.

1,3-Benzo­thia­zin-4-ones (BTZs) are a promising new class of drugs with activity against Mycobacterium tuberculosis, which have already reached clinical trials. A product obtained in low yield upon treatment of 8-nitro-2-(piperidin-1-yl)-6-(tri­fluoro­meth­yl)-4H-benzo­thia­zin-4-one with 3-chloro­perbenzoic acid, in ana­logy to a literature report describing the formation of sulfoxide and sulfone derived from BTZ043 [Tiwari et al. (2015 ▸). ACS Med. Chem. Lett.6, 128–133], is a ring-contracted benziso­thia­zolinone (BIT) 1-oxide, namely, 7-nitro-2-(piperi­dine-1-carbon­yl)-5-(tri­fluoro­meth­yl)benzo[d]iso­thia­zol-3(2H)-one 1-oxide, C₁₄H₁₂F₃N₃O₅S, as revealed by X-ray crystallography. Single-crystal X-ray analysis of the oxidation product originally assigned as BTZ043 sulfone provides clear evidence that the structure of the purported BTZ043 sulfone is likewise the corresponding BIT 1-oxide, namely, 2-[(S)-2-methyl-1,4-dioxa-8-aza­spiro­[4.5]decane-8-carbon­yl]-7-nitro-5-(tri­fluoro­meth­yl)benzo[d]iso­thia­zol-3(2H)-one 1-oxide, C₁₇H₁₆F₃N₃O₇S. A possible mechanism for the ring contraction affording the BIT 1-oxides instead of the anti­cipated constitutionally isomeric BTZ sulfones and anti­mycobacterial activities thereof are discussed.

Factors associated with the contemplative stage of readiness to initiate osteoporosis treatment

We investigated the factors associated with readiness for initiating osteoporosis treatment in women at high risk of fracture. We found that women in the contemplative stage were more likely to report previously being told having osteoporosis or osteopenia, acknowledge concern about osteoporosis, and disclose prior osteoporosis treatment.

INTRODUCTION

Understanding factors associated with reaching the contemplative stage of readiness to initiate osteoporosis treatment may inform the design of behavioral interventions to improve osteoporosis treatment uptake in women at high risk for fracture.

METHODS

We measured readiness to initiate osteoporosis treatment using a modified form of the Weinstein Precaution Adoption Process Model (PAPM) among 2684 women at high risk of fracture from the Activating Patients at Risk for OsteoPOroSis (APROPOS) clinical trial. Pre-contemplative participants were those who self-classified in the unaware and unengaged stages of PAPM (stages 1 and 2). Contemplative participants were those in the undecided, decided not to act, or decided to act stages of PAPM (stages 3, 4, and 5). Using multivariable logistic regression, we evaluated participant characteristics associated with levels of readiness to initiate osteoporosis treatment.

RESULTS

Overall, 24% (N = 412) self-classified in the contemplative stage of readiness to initiate osteoporosis treatment. After adjusting for age, race, education, health literacy, and major osteoporotic fracture in the past 12 months, contemplative women were more likely to report previously being told they had osteoporosis or osteopenia (adjusted odds ratio [aOR] (95% CI) 11.8 (7.8-17.9) and 3.8 (2.5-5.6), respectively), acknowledge concern about osteoporosis (aOR 3.5 (2.5-4.9)), and disclose prior osteoporosis treatment (aOR 4.5 (3.3-6.3)) than women who self-classified as pre-contemplative.

CONCLUSIONS

For women at high risk for future fractures, ensuring women's recognition of their diagnosis of osteoporosis/osteopenia and addressing their concerns about osteoporosis are critical components to consider when attempting to influence stage of behavior transitions in osteoporosis treatment.

Intracellular and in vivo evaluation of imidazo[2,1-b]thiazole-5-carboxamide anti-tuberculosis compounds

The imidazo[2,1-b]thiazole-5-carboxamides (ITAs) are a promising class of anti-tuberculosis agents shown to have potent activity in vitro and to target QcrB, a key component of the mycobacterial cytochrome bcc-aa3 super complex critical for the electron transport chain. Herein we report the intracellular macrophage potency of nine diverse ITA analogs with MIC values ranging from 0.0625-2.5 μM and mono-drug resistant potency ranging from 0.0017 to 7 μM. The in vitro ADME properties (protein binding, CaCo-2, human microsomal stability and CYP450 inhibition) were determined for an outstanding compound of the series, ND-11543. ND-11543 was tolerable at >500 mg/kg in mice and at a dose of 200 mg/kg displayed good drug exposure in mice with an AUC(0-24h) >11,700 ng·hr/mL and a >24 hr half-life. Consistent with the phenotype observed with other QcrB inhibitors, compound ND-11543 showed efficacy in a chronic murine TB infection model when dosed at 200 mg/kg for 4 weeks. The efficacy was not dependent upon exposure, as pre-treatment with a known CYP450-inhibitor did not substantially improve efficacy. The ITAs are an interesting scaffold for the development of new anti-TB drugs especially in combination therapy based on their favorable properties and novel mechanism of action.

Deuteration of BTZ043 Extends the Lifetime of Meisenheimer Intermediates to the Antituberculosis Nitroso Oxidation State

Substituted nitrobenzothiazinones (BTZs) are potent antituberculosis prodrugs that are reductively activated to produce nitroso moieties that form covalent adducts with a cysteine residue of decaprenylphosphoryl-β-d-ribose-2'-oxidase (DprE1) of Mycobacterium tuberculosis (Mtb). The resulting cell wall synthesis inhibition is lethal to Mtb, leading to consideration of development of BTZs for clinical use. The hydride-induced reduction of the nitroaromatic proceeds by reversible formation of the corresponding Meisenheimer complex. Herein we demonstrate that chemical reduction of BTZ043 with NaBD₄ followed by reoxidation incorporates deuterium into the core nitro aromatic warhead. Subsequent reduction of the deuterated species is not affected, but, as expected, reoxidation is slowed by the deuterium isotope effect, thus prolonging the lifetime of the active nitroso oxidation state.

Carbon metabolism modulates the efficacy of drugs targeting the cytochrome bc1:aa3 in Mycobacterium tuberculosis

The influence of carbon metabolism on oxidative phosphorylation is poorly understood in mycobacteria. M. tuberculosis expresses two respiratory terminal oxidases, the cytochrome bc₁:aa₃ and the cytochrome bd oxidase, which are jointly required for oxidative phosphorylation and mycobacterial viability. The essentiality of the cytochrome bc₁:aa₃ for optimum growth is illustrated by its vulnerability to chemical inhibition by the clinical drug candidate Q203 and several other chemical series. The cytochrome bd oxidase is not strictly essential for growth but is required to maintain bioenergetics when the function of the cytochrome bc₁:aa₃ is compromised. In this study, we observed that the potency of drugs targeting the cytochrome bc₁:aa₃ is influenced by carbon metabolism. The efficacy of Q203 and related derivatives was alleviated by glycerol supplementation. The negative effect of glycerol supplementation on Q203 potency correlated with an upregulation of the cytochrome bd oxidase-encoding cydABDC operon. Upon deletion of cydAB, the detrimental effect of glycerol on the potency of Q203 was abrogated. The same phenomenon was also observed in recent clinical isolates, but to a lesser extent compared to the laboratory-adapted strain H37Rv. This study reinforces the importance of optimizing in vitro culture conditions for drug evaluation in mycobacteria, a factor which appeared to be particularly essential for drugs targeting the cytochrome bc₁:aa₃ terminal oxidase.

Clinical presentation of delayed hemolytic transfusion reactions and hyperhemolysis in sickle cell disease

Red blood cell (RBC) transfusion therapy is a key component in the comprehensive management of patients with sickle cell disease (SCD). Consequently, most adult SCD patients will receive at least one, and many will receive more than a hundred RBC transfusions in their lifetime. SCD patients develop RBC alloantibodies much more frequently than non-SCD transfused patients, which often make the selection of compatible RBCs extremely difficult, in addition to placing patients at significantly higher risk of suffering from delayed hemolytic transfusion reactions (DHTRs). Similar to alloimunization, DHTRs are much more common in patients with SCD compared to other heavily transfused populations, and are particularly consequential due to their propensity to cause hyperhemolysis, a life-threatening phenomenon in which both transfused RBCs in addition to the patient's own sickle-erythrocytes are destroyed. In this review, we highlight the incidence and pathophysiology of DHTRs; illustrate common presentations, appropriate evaluations and outcomes of DHTRs in patients with SCD; and discuss strategies for preventing or reducing the likelihood of DHTRs from occurring.

Whole-cell biosensing by siderophore-based molecular recognition and localized surface plasmon resonance

A siderophore-based active bacterial pull-down strategy was integrated in a localized surface plasmon resonance (LSPR) sensing platform and subsequently tested by detecting whole-cell Acinetobacter baumannii. The LSPR-based whole-cell sensing approach was previously demonstrated with aptamer-based molecular recognition motifs, and here it is extended to the powerful siderophore system, which exploits the natural bacterial need to sequester Fe(III). Specifically, a biscatecholate-monohydroxamate mixed ligand siderophore linked to a biotin via three polyethylene glycol repeating units was synthesized and immobilized on Au trigonal nanoprisms of an LSPR sensor. The resulting surface-confined biotinylated siderophore subsequently chelated Fe(III), forming a siderophore-Fe(III) complex which was shown to be competent to recognize A. baumannii. Target bacteria were captured and then detected by measuring wavelength shifts in the LSPR extinction spectrum. This siderophore pull-down LSPR biosensor approach is rapid (≤3 h detection) and sensitive - with a limit of detection (LOD) of 80 bacterial cells and a linear wavelength shift over the range 4 × 10² to 4 × 10⁶ cfu mL^-1. As intended by design, the siderophore-based biosensor was selective for A. baumannii over Pseudomonas aeruginosa, Escherichia coli, and Bacillus cereus, and was stable in ambient conditions for up to 2 weeks.

Targeting the Mycobacterium ulcerans cytochrome bc1:aa3 for the treatment of Buruli ulcer

Mycobacterium ulcerans is the causative agent of Buruli ulcer, a neglected tropical skin disease that is most commonly found in children from West and Central Africa. Despite the severity of the infection, therapeutic options are limited to antibiotics with severe side effects. Here, we show that M. ulcerans is susceptible to the anti-tubercular drug Q203 and related compounds targeting the respiratory cytochrome bc₁:aa₃. While the cytochrome bc₁:aa₃ is the primary terminal oxidase in Mycobacterium tuberculosis, the presence of an alternate bd-type terminal oxidase limits the bactericidal and sterilizing potency of Q203 against this bacterium. M. ulcerans strains found in Buruli ulcer patients from Africa and Australia lost all alternate terminal electron acceptors and rely exclusively on the cytochrome bc₁:aa₃ to respire. As a result, Q203 is bactericidal at low dose against M. ulcerans replicating in vitro and in mice, making the drug a promising candidate for Buruli ulcer treatment.

Mycobacterium ulcerans is the causative agent of Buruli ulcer (BU). Existing anti-tubercular drugs have been used to treat the condition with varying success. Here, the authors show that a clinical-stage drug candidate for tuberculosis, Q203, is effective at killing M. ulcerans and is a promising therapeutic candidate for BU.

Siderophore Conjugates of Daptomycin are Potent Inhibitors of Carbapenem Resistant Strains of Acinetobacter baumannii

Development of resistance to antibiotics is a major medical problem. One approach to extending the utility of our limited antibiotic arsenal is to repurpose antibiotics by altering their bacterial selectivity. Many antibiotics that are used to treat infections caused by Gram-positive bacteria might be made effective against Gram-negative bacterial infections, if they could circumvent permeability barriers and antibiotic deactivation processes associated with Gram-negative bacteria. Herein, we report that covalent attachment of the normally Gram-positive-only antibiotic, daptomycin, with iron sequestering siderophore mimetics that are recognized by Gram-negative bacteria, provides conjugates that are active against virulent strains of Acinetobacter baumannii, including carbapenemase and cephalosporinase producers. The result is the generation of a new set of antibiotics designed to target bacterial infections that have been designated as being of dire concern.

A Synthetic Dual Drug Sideromycin Induces Gram-Negative Bacteria To Commit Suicide with a Gram-Positive Antibiotic

Many antibiotics lack activity against Gram-negative bacteria because they cannot permeate the outer membrane or suffer from efflux and, in the case of β-lactams, are degraded by β-lactamases. Herein, we describe the synthesis and studies of a dual drug conjugate (1) of a siderophore linked to a cephalosporin with an attached oxazolidinone. The cephalosporin component of 1 is rapidly hydrolyzed by purified ADC-1 β-lactamase to release the oxazolidinone. Conjugate 1 is active against clinical isolates of Acinetobacter baumannii as well as strains producing large amounts of ADC-1 β-lactamase. Overall, the results are consistent with siderophore-mediated active uptake, inherent activity of the delivered dual drug, and in the presence of β-lactamases, intracellular release of the oxazolidinone upon cleavage of the cephalosporin to allow the freed oxazolidinone to inactivate its target. The ultimate result demonstrates that Gram-positive oxazolidinone antibiotics can be made to be effective against Gram-negative bacteria by β-lactamase triggered release.

Methodology for Monobactam Diversification: Syntheses and Studies of 4-Thiomethyl Substituted β-Lactams with Activity against Gram-Negative Bacteria, Including Carbapenemase Producing Acinetobacter baumannii

Bromine induced lactamization of vinyl acetohydroxamates facilitated syntheses of monocyclic β-lactams suitable for incorporation of a thiomethyl and extended functionality at the C(4) position. Elaboration of the resulting substituted N-hydroxy-2-azetidinones allowed incorporation of functionalized α-amino substituents appropriate for enhancement of antibiotic activity. Evaluation of antibacterial activity against a panel of Gram-positive and Gram-negative bacteria revealed structure-activity relationships (SAR) and identification of potent new monobactam antibiotics. The corresponding bis-catechol conjugate, 42, has excellent activity against Gram-negative bacteria including carbapenemase and carbacephalosporinase producing strains of Acinetobacter baumannii, which have been listed by the WHO as being of critical concern worldwide.

Preparation and Evaluation of Potent Pentafluorosulfanyl-Substituted Anti-Tuberculosis Compounds

The global fight to stop tuberculosis (TB) remains a great challenge, particularly with the increase in drug-resistant strains and a lack of funding to support the development of new treatments. To bolster a precarious drug pipeline, we prepared a focused panel of eight pentafluorosulfanyl (SF₅ ) compounds which were screened for their activity against Mycobacterium tuberculosis (Mtb) H37Rv in three different assay conditions and media. All eight compounds had sub-micromolar potency, and four displayed MICs <100 nm. Seven compounds were evaluated against non-replicating and mono-drug-resistant Mtb, and for their ability to inhibit Mtb within the macrophage. The greatest potency was observed against intracellular Mtb (MIC <10 nm for three compounds), which is often the most challenging to target. In general, the SF₅ -bearing compounds were very similar to their CF₃ counterparts, with the major differences observed being their in vitro ADME properties. Two SF₅ -bearing compounds were found to have greater protein binding than their corresponding CF₃ counterparts, but were also less metabolized in human microsomes, resulting in longer half-lives.

In Vivo Dearomatization of the Potent Antituberculosis Agent BTZ043 via Meisenheimer Complex Formation

Nitrobenzothiazinones are among the most potent antituberculosis agents. Herein, we disclose an unprecedented in vivo reduction process that affords Meisenheimer complexes of the clinical candidates BTZ043 and PBTZ169. The reduction is reversible, occurs in all mammalian species investigated, has a profound influence on the in vivo ADME characteristics, and has considerable implications for the design and implementation of clinical studies. The reduction was confirmed by chemical studies that enabled the complete characterization of the Meisenheimer complex and its subsequent chemistry. Combination of the in vivo and chemical studies with LC-MS characterization and assay development also provides a basis for rational lead optimization of this very promising class of antituberculosis agents.

Stereo- and regioselectivity of the hetero-Diels-Alder reaction of nitroso derivatives with conjugated dienes

The hetero-Diels-Alder reaction between a nitroso dienophile and a conjugated diene to give the 3,6-dihydro-2H-1,2-oxazine scaffold is useful for the synthesis of many biologically interesting molecules due to the diverse opportunities created by subsequent transformations of the resulting 1,2-oxazine ring. This review discusses the rationale for the observed regio- and stereoselectivity and the methods developed in recent years used to control and improve the stereo- and regioselectivity for the synthesis of 1,2-oxazine scaffolds.

Arrival of Imidazo[2,1-b]thiazole-5-carboxamides: Potent Anti-tuberculosis Agents That Target QcrB

Increasing interest in the potent anti-tuberculosis activity and the novel target (QcrB) of imidazo[1,2-a]pyridine-3-carboxamides encouraged extended structure-activity relationship studies of additional scaffolds. This study reports on the in vitro profiling of the imidazo[2,1-b]thiazole-5-carboxamides as a new promising class of anti-tuberculosis compounds endowed with nanomolar potency against replicating and drug-resistant Mycobacterium tuberculosis (Mtb) as well as low toxicity to VERO cells. Compounds 6, 16, and 17 had MIC values <10 nM and toxicity >100 μM. On-target selectivity of this series was confirmed by cross-resistance of specific QcrB mutants as well as the hypersusceptibility of a mutant with a functional gene deletion of the alternative cytochrome bd oxidase. Additionally, to demonstrate selectivity, three analogues (6, 15, 17) were broadly screened against a diverse set of eight strains of bacteria, including both Gram-positive and Gram-negative as well as six disease-causing non-tuberculosis mycobacteria. Finally, compounds 16 and 17 were found to be active in macrophages infected with Mtb.

Design, Syntheses, and Anti-TB Activity of 1,3-Benzothiazinone Azide and Click Chemistry Products Inspired by BTZ043

Electron deficient nitroaromatic compounds such as BTZ043 and its closest congener, PBTZ169, and related agents are a promising new class of anti-TB compounds. Herein we report the design and syntheses of 1,3-benzothiazinone azide (BTZ-N3) and related click chemistry products based on the molecular mode of activation of BTZ043. Our computational docking studies indicate that BTZ-N3 binds in the essentially same pocket as that of BTZ043. Detailed biochemical studies with cell envelope enzyme fractions of Mycobacterium smegmatis combined with our model biochemical reactivity studies with nucleophiles indicated that, in contrast to BTZ043, the azide analogue may have a different mode of activation for anti-TB activity. Subsequent enzymatic studies with recombinant DprE1 from Mtb followed by MIC determination in NTB1 strain of Mtb (harboring Cys387Ser mutation in DprE1 and is BTZ043 resistant) unequivocally indicated that BTZ-N3 is an effective reversible and noncovalent inhibitor of DprE1.

Design, syntheses, and anti-tuberculosis activities of conjugates of piperazino-1,3-benzothiazin-4-ones (pBTZs) with 2,7-dimethylimidazo [1,2-a]pyridine-3-carboxylic acids and 7-phenylacetyl cephalosporins

Tuberculosis (TB) remains one of the most threatening diseases in the world and the need for development of new therapies is dire. Herein we describe the rationale for the design and subsequent syntheses and studies of conjugates between pBTZ and both the imidazopyridine and cephalosporin scaffolds. Overall some compounds exhibited notable anti-TB activity in the range of 2-0.2 μM in the Microplate Alamar Blue (MABA) Assay.

Syntheses and Biological Evaluations of Highly Functionalized Hydroxamate Containing and N-Methylthio Monobactams as Anti-Tuberculosis and β-Lactamase Inhibitory Agents

Both the resurgence of tuberculosis (TB) and antibiotic resistance continue to threaten modern healthcare and new means of combating pathogenic bacterial infections are needed. The syntheses of monobactams possessing hydroxamate and N-methylthio functionality are described, as well as their anti-TB, in vitro β-lactamase inhibitory, and general antimicrobial evaluations. A number of compounds exhibited significant anti-TB and β-lactamase inhibitory activity, with MIC values in the range of 25 to < 0.19 μM against Mycobacteria tuberculosis (M.tb), and K_i values in the range of 25-0.03 μM against purified NDM-1 and VIM-1 lystate metallo β-lactamases. This work suggests that these scaffolds may serve as promising leads in developing new antibiotics and/or β-lactamase inhibitors.

Syntheses and studies of new forms of N-sulfonyloxy β-lactams as potential antibacterial agents and β-lactamase inhibitors

The synthesis of a small library of N-sulfonyloxy-2-azetidinones is reported and the preliminary results of the investigation of the biological activity of these molecules are discussed. These new multi-electrophilic β-lactams ('electrophilic bombs') display unexpected selectivity in their antibacterial activity and β-lactamase inhibitory activity.

Syntheses and Antibacterial Activity of N-Acylated Ciprofloxacin Derivatives Based on the Trimethyl Lock

Several N-acyl ciprofloxacin quinone derivatives based on a trimethyl lock structure were synthesized, and their in vitro antibacterial activity against a panel of clinically relevant bacteria was evaluated. A few new analogues displayed enhanced activity against Gram-positive species compared to the parent drug. Additionally, studies of 8-Cip, which was the most potent compound tested, indicate that it may act through a dual-action mechanism.

Siderophore-fluoroquinolone conjugates containing potential reduction-triggered linkers for drug release: synthesis and antibacterial activity

Syntheses of two Siderophore-fluoroquinolone conjugates with a potential reduction triggered linker for drug release are described. The "trimethyl lock" based linker incorporated in the conjugates was designed to be activated by taking advantage of the reductive pathway of bacterial iron metabolism. Electrochemical and LC-MS studies indicated that the linker is thermodynamically reducible by common biological reductants and the expected lactonization proceeds rapidly with concomitant release of the drug. Antibacterial activity assays revealed that conjugates with the reduction-triggered linker were more potent than their counterparts with a stable linker, which suggests that drug release occurs inside bacterial cells.

Syntheses and evaluation of substituted aromatic hydroxamates and hydroxamic acids that target Mycobacterium tuberculosis

Tuberculosis (TB) continues to remain one of the most threatening diseases in the world. With the emergence of multi-drug resistant (MDR) and extensively drug resistant (XDR) strains, the need to develop new therapies is dire. The syntheses of a focused library of hydroxamates and hydroxamic acids is described, as well as anti-TB activity in the microplate alamar blue assay (MABA). A number of compounds exhibited good activity against Mtb, with notable compounds exhibiting MIC values in the range of 20-0.71 μM. This work suggests that both hydroxamates and their free acids may be incorporated into more complex scaffolds and serve as potential leads for the development of anti-TB agents.

Tetrahydrofuranyl and tetrahydropyranyl protection of amino acid side-chains enables synthesis of a hydroxamate-containing aminoacylated tRNA

The ability to specifically engineer metal binding sites into target proteins has far-reaching consequences ranging from the development of new biocatalysts and imaging reagents to the production of proteins with increased stability. We report the efficient tRNA-mediated incorporation of the hydroxamate containing amino acid, N(ε)-acetyl-N(ε)-hydroxy-L-lysine, into a transcription factor (TFIIIA). Because this amino acid is compact, hydrophilic, and uncharged at physiological pH, it should have little or no effect on protein folding or solubility. The N(ε)-hydroxy group of the hydroxamate is refractory to photodeprotection and required the identification of reagents for O-protection that are compatible with the synthesis of acylated tRNA. Tetrahydrofuranyl and tetrahydropyranyl O-protecting groups can be removed using mild acid conditions and allowed for an orthogonal protection strategy in which deprotection of the amino acid side chain precedes ligation of an acylated dinucleotide to a truncated suppressor tRNA. These protecting groups will provide a valuable alternative for O-protection, especially in cases where photodeprotection cannot be used.

Putting Tuberculosis (TB) To Rest: Transformation of the Sleep Aid, Ambien, and "Anagrams" Generated Potent Antituberculosis Agents

Zolpidem (Ambien, 1) is an imidazo[1,2-a]pyridine-3-acetamide and an approved drug for the treatment of insomnia. As medicinal chemists enamored by how structure imparts biological function, we found it to have strikingly similar structure to the antitubercular imidazo[1,2-a]pyridine-3-carboxyamides. Zolpidem was found to have antituberculosis activity (MIC of 10–50 μM) when screened against replicating Mycobacterium tuberculosis (Mtb) H₃₇Rv. Manipulation of the Zolpidem structure, notably, to structural isomers (“anagrams”), attains remarkably improved potency (5, MIC of 0.004 μM) and impressive potency against clinically relevant drug-sensitive, multi- and extensively drug-resistant Mtb strains (MIC < 0.03 μM). Zolpidem anagrams and analogues were synthesized and evaluated for their antitubercular potency, toxicity, and spectrum of activity against nontubercular mycobacteria and Gram-positive and Gram-negative bacteria. These efforts toward the rational design of isomeric anagrams of a well-known sleep aid underscore the possibility that further optimization of the imidazo[1,2-a]pyridine core may well “put TB to rest”.

Syntheses and Antituberculosis Activity of 1,3-Benzothiazinone Sulfoxide and Sulfone Derived from BTZ043

The discovery of 1,3-benzothiazin-4-ones (BTZs), especially BTZ043 and PBTZ-169 as potent agents for the treatment of tuberculosis, prompted intensive research related to development of potential antituberculosis agents based on electron deficient nitroaromatic scaffolds. Herein we report the syntheses, computational and NMR studies and anti-TB activity of oxidation products, 1,3-benzothiazinone sulfoxide (BTZ-SO) and 1,3-benzothiazinone sulfone (BTZ-SO2) derived from BTZ043. The combined computational and NMR work revealed differences in the total charge densities and molecular shapes of the oxidation products. While docking studies still suggested similar interactions and binding patterns for both products with the target DprE1 enzyme, antituberculosis assays indicated remarkable differences in their activity. Interestingly, BTZ-SO possesses potent activity against nonpathogenic and pathogenic mycobacterial strains, but BTZ-SO2 is only weakly active.

Nitroso Diels-Alder (NDA) reaction as an efficient tool for the functionalization of diene-containing natural products

This review describes the use of nitroso Diels-Alder reactions for the functionalization of complex diene-containing natural products in order to generate libraries of compounds with potential biological activity. The application of this methodology to the structural modification of a series of natural products (thebaine, steroidal dienes, rapamycin, leucomycin, colchicine, isocolchicine and piperine) is discussed using relevant examples from the literature from 1973 onwards. The biological activity of the resulting compounds is also discussed. Additional comments are provided that evaluate the methodology as a useful tool in organic, bioorganic and medicinal chemistry.

Scaffold-switching: an exploration of 5,6-fused bicyclic heteroaromatics systems to afford antituberculosis activity akin to the imidazo[1,2-a]pyridine-3-carboxylates

A set of 5,6-fused bicyclic heteroaromatic scaffolds were investigated for their in vitro anti-tubercular activity versus replicating and non-replicating strains of Mycobacterium tuberculosis (Mtb) in an attempt to find an alternative scaffold to the imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrimidines that were previously shown to have potent activity against replicating and drug resistant Mtb. The five new bicyclic heteroaromatic scaffolds explored in this study include a 2,6-dimethylimidazo[1,2-b]pyridazine-3-carboxamide (7), a 2,6-dimethyl-1H-indole-3-carboxamide (8), a 6-methyl-1H-indazole-3-carboxamide (9), a 7-methyl-[1,2,4]triazolo[4,3-a]pyridine-3-carboxamide (10), and a 5,7-dimethyl-[1,2,4]triazolo[1,5-a]pyrimidine-2-carboxamide (11). Additionally, imidazo[1,2-a]pyridines isomers (2 and 12) and a homologous imidazo[1,2-a]pyrimidine isomer (6) were prepared and compared. Compounds 2 and 6 were found to be the most potent against H37Rv Mtb (MIC's of 0.1 μM and 1.3 μM) and were inactive (MIC >128 μM) against Staphylococcus aureus, Escherichia coli and Candida albicans. Against other non-tubercular mycobacteria strains, compounds 2 and 6 had activity against Mycobacterium avium (16 and 122 μM, respectively), Mycobacterium kansasii (4 and 19 μM, respectively), Mycobacterium bovis BCG (1 and 8 μM, respectively) while all the other scaffolds were inactive (>128 μM).

Design and Syntheses of Anti-Tuberculosis Agents Inspired by BTZ043 Using a Scaffold Simplification Strategy

Tuberculosis (TB), a disease caused by Mycobacterium tuberculosis (Mtb), is a global public health concern because of the emergence of various resistant strains. Benzothiazin-4-ones (BTZs), represented by BTZ043, are a promising new class of agents for the treatment of tuberculosis and have been shown to kill Mtb in vitro, ex vivo, and in mouse models of TB. Herein we report the design and syntheses of nitroaromatic sulfonamide, reverse-amide, and ester classes of anti-TB agents using a scaffold simplification strategy based on BTZ043. The presented work explores the effect of functional groups such as sulfonamides, reverse-amides, and esters that are attached to the nitroaromatic rings on their anti-TB activity. The in vitro activity of the compounds evaluated against the H37Rv strain of Mtb show that nitroaromatic sulfonamides and nitrobenzoic acid esters with two nitro substituents were most active and highlights the importance of the electronic character (electron deficient aromatic ring) of the nitroaromatic ring as a central theme in these types of nitroaromatic anti-TB agents.

Bactericidal activity of an imidazo[1, 2-a]pyridine using a mouse M. tuberculosis infection model

Tuberculosis remains a global threat due in part to the long treatment regimen and the increased prevalence of drug resistant M. tuberculosis strains. Therefore, new drug regimens are urgently required to combat this deadly disease. We previously synthesized and evaluated a series of new anti-tuberculosis compounds which belong to the family of imidazo[1,2-a]pyridines. This family of compounds showed low nM MIC (minimal inhibitory concentration) values against M. tuberculosis in vitro. In this study, a derivative of imidazo[1,2-a]pyridines, (N-(4-(4-chlorophenoxy)benzyl)-2,7-dimethylimidazo[1,2-a]pyridine-3-carboxamide) (ND-09759), was selected as a promising lead compound to determine its protective efficacy using a mouse infection model. Pharmacokinetic analysis of ND-09759 determined that at a dosage of 30 mg/kg mouse body weight (PO) gave a maximum serum drug concentration (C_max) of 2.9 µg/ml and a half-life of 20.1 h. M. tuberculosis burden in the lungs and spleens was significantly decreased in mice treated once daily 6 days per week for 4-weeks with ND-09759 compared to untreated mice and this antibiotic activity was equivalent to isoniazid (INH) and rifampicin (RMP), two first-line anti-TB drugs. We observed slightly higher efficacy when using a combination of ND-09759 with either INH or RMP. Finally, the histopathological analysis revealed that infected mice treated with ND-09759 had significantly reduced inflammation relative to untreated mice. In conclusion, our findings indicate ND-09759 might be a potent candidate for the treatment of active TB in combination with current standard anti-TB drugs.

Advancement of Imidazo[1,2-a]pyridines with Improved Pharmacokinetics and Nanomolar Activity Against Mycobacterium tuberculosis

A set of fourteen imidazo[1,2-a]pyridine-3-carboxamides was synthesized and screened against Mycobacterium tuberculosis H₃₇Rv. The minimum inhibitory concentrations of twelve of these agents were ≤ 1 μM against replicating bacteria and five compounds (9, 12, 16, 17 and 18) had MIC values ≤ 0.006 μM. Compounds 13 and 18 were screened against a panel of MDR and XDR drug resistant clinical Mtb strains with the potency of 18 surpassing that of clinical candidate PA-824 by nearly 10 fold. The in vivo pharmacokinetics of compounds 13 and 18 were evaluated in male mice by oral (PO) and intravenous (IV) routes. These results indicate that readily synthesized imidazo[1,2-a]pyridine-3-carboxamides are an exciting new class of potent, selective anti-TB agents that merit additional development opportunities.

Biscatecholate-monohydroxamate mixed ligand siderophore-carbacephalosporin conjugates are selective sideromycin antibiotics that target Acinetobacter baumannii

Chemical syntheses and biological evaluation of biscatecholate-monohydroxamate mixed ligand sideromycins utilizing the carbacephalosporin β-lactam antibiotic loracarbef and the fluoroquinolone antibiotic ciprofloxacin are described. The mixed ligand β-lactam sideromycin (1b) had remarkably selective and extremely potent antibacterial activity against the Gram-negative pathogen Acinetobacter baumannii ATCC 17961 (MIC = 0.0078 μM). The antibacterial activity of the β-lactam sideromycin was inversely related to the iron(III) concentration in the testing media and was antagonized by the presence of the competing parent siderophore. These data suggested that active transport of the mixed ligand β-lactam sideromycin across the outer cell membrane of A. baumannii via siderophore-uptake pathways was responsible for the selective and potent antibacterial activity.