Exploring Scaffold Hopping for Novel 2-(Quinolin-4-yloxy)acetamides with Enhanced Antimycobacterial Activity

Utilizing a scaffold-hopping strategy from the drug candidate telacebec, a novel series of 2-(quinolin-4-yloxy)acetamides was synthesized and evaluated as inhibitors of Mycobacterium tuberculosis (Mtb) growth. These compounds demonstrated potent activity against drug-sensitive and multidrug-resistant strains (MIC ≤ 0.02 μM). Leading compounds were evaluated against a known qcrB resistant strain (T313A), and their loss in activity suggested that the cytochrome bc1 complex is the likely target. Additionally, these structures showed high selectivity regarding mammalian cells (selectivity index > 500) and stability across different aqueous media. Furthermore, some of the synthesized quinolines demonstrated aqueous solubility values that exceeded those of telacebec, while maintaining low rates of metabolism. Finally, a selected compound prevented Mtb growth by more than 1.7 log10 colony forming units in a macrophage model of tuberculosis (TB) infection. These findings validate the proposed design and introduce new 2-(quinolin-4-yloxy)acetamides with potential for development in TB drug discovery campaigns.

Identification of potential inhibitors of Mycobacterium tuberculosis shikimate kinase: molecular docking, in silico toxicity and in vitro experiments

Tuberculosis (TB) is one of the main causes of death from a single pathological agent, Mycobacterium tuberculosis (Mtb). In addition, the emergence of drug-resistant TB strains has exacerbated even further the treatment outcome of TB patients. It is thus needed the search for new therapeutic strategies to improve the current treatment and to circumvent the resistance mechanisms of Mtb. The shikimate kinase (SK) is the fifth enzyme of the shikimate pathway, which is essential for the survival of Mtb. The shikimate pathway is absent in humans, thereby indicating SK as an attractive target for the development of anti-TB drugs. In this work, a combination of in silico and in vitro techniques was used to identify potential inhibitors for SK from Mtb (MtSK). All compounds of our in-house database (Centro de Pesquisas em Biologia Molecular e Funcional, CPBMF) were submitted to in silico toxicity analysis to evaluate the risk of hepatotoxicity. Docking experiments were performed to identify the potential inhibitors of MtSK according to the predicted binding energy. In vitro inhibitory activity of MtSK-catalyzed chemical reaction at a single compound concentration was assessed. Minimum inhibitory concentration values for in vitro growth of pan-sensitive Mtb H37Rv strain were also determined. The mixed approach implemented in this work was able to identify five compounds that inhibit both MtSK and the in vitro growth of Mtb.

Antitubercular Activity of Novel 2-(Quinoline-4-yloxy)acetamides with Improved Drug-Like Properties

Using cycloalkyl and electron-donating groups to decrease the carbonyl electrophilicity, a novel series of 2-(quinoline-4-yloxy)acetamides was synthesized and evaluated as in vitro inhibitors of Mycobacterium tuberculosis (Mtb) growth. Structure-activity relationship studies led to selective and potent antitubercular agents with minimum inhibitory concentrations in the submicromolar range against drug-sensitive and drug-resistant Mtb strains. An evaluation of the activity of the lead compounds against a spontaneous qcrB mutant strain indicated that the structures targeted the cytochrome bc 1 complex. In addition, selected molecules inhibited Mtb growth in a macrophage model of tuberculosis infection. Furthermore, the leading compound was chemically stable depending on the context and showed good kinetic solubility, high permeability, and a low rate of in vitro metabolism. Finally, the pharmacokinetic profile of the compound was assessed after oral administration to mice. To the best of our knowledge, for the first time, a 2-(quinoline-4-yloxy)acetamide was obtained with a sufficient exposure, which may enable in vivo effectiveness and its further development as an antituberculosis drug candidate.

Ultrasound-Assisted Synthesis of 4-Alkoxy-2-methylquinolines: An Efficient Method toward Antitubercular Drug Candidates

Tuberculosis (TB) has been described as a global health crisis since the second half of the 1990s. Mycobacterium tuberculosis (Mtb), the etiologic agent of TB in humans, is a very successful pathogen, being the main cause of death in the population among infectious agents. In 2019, it was estimated that around 10 million individuals were contaminated by this bacillus and about 1.2 million succumbed to the disease. In recent years, our research group has reported the design and synthesis of quinoline derivatives as drug candidates for the treatment of TB. These compounds have demonstrated potent and selective growth inhibition of drug-susceptible and drug-resistant Mtb strains. Herein, a new synthetic approach was established providing efficient and rapid access (15 min) to a series of 4-alkoxy-6-methoxy-2-methylquinolines using ultrasound energy. The new synthetic protocol provides a simple procedure utilizing an open vessel system that affords the target products at satisfactory yields (45–84%) and elevated purities (≥95%). The methodology allows the evaluation of a larger number of molecules in assays against the bacillus, facilitating the determination of the structure–activity relationship with a reduced environmental cost.

Design, synthesis, and evaluation of new 2-(quinoline-4-yloxy)acetamide-based antituberculosis agents

Using a classical molecular simplification approach, a series of 36 quinolines were synthesized and evaluated as in vitro inhibitors of Mycobacterium tuberculosis (M. tuberculosis) growth. Structure-activity relationship (SAR) studies leaded to potent antitubercular agents, with minimum inhibitory concentration (MIC) values as low as 0.3 μM against M. tuberculosis H37Rv reference strain. Furthermore, the lead compounds were active against multidrug-resistant strains, without cross-resistance with some first- and second-line drugs. Testing the molecules against a spontaneous mutant strain containing a single mutation in the qcrB gene (T313A) indicated that the synthesized quinolines targeted the cytochrome bc₁ complex. In addition, leading compounds were devoid of apparent toxicity to HepG2 and Vero cells and showed moderate elimination rates in human liver S9 fractions. Finally, the selected structures inhibited M. tuberculosis growth in a macrophage model of tuberculosis infection. Taken together, these data indicate that this class of compounds may furnish candidates for the future development of antituberculosis drugs.