5-Fluoroindole Reduces the Bacterial Burden in a Murine Model of Mycobacterium tuberculosis Infection.

Tuberculosis is a disease caused by a single pathogen that leads to a death toll estimated to be more than a million per year. Mycobacterium tuberculosis (Mtb), which affects mainly the lungs, spreads by airborne transmission when infectious respiratory particles from an infected human enter the respiratory tract of another person. Despite diagnosis and treatment being well established, the rise of cases of patients infected with Mtb strains with multidrug resistance to the antibiotics used in the regimen against the disease is alarming. Indole used as a core molecule has been described as a promising structure to treat several diseases. 5-Fluoroindole (5-FI) compound, evaluated in the free base and in the hydrochloride (5-FI.HCl) forms, inhibited the growth of pan-sensitive Mtb H37Rv strain in the same range (4.7-29.1 µM) of clinical isolates that have resistance to at least two first-line drugs. Although 5-FI showed no cytotoxicity in Vero and HepG2 cells, high permeability (2.4.10-6 cm/s) in the PAMPA assay, and high metabolic stability (Clint 9.0 mL/min/kg) in rat liver microsomes, limited solubility at plasmatic and intestinal pH values prompted formation and employment of its salt form (5-FI.HCl). Although the 5-FI.HCl compound showed increased solubility at pH values of 7.4 and 9.1 and increased stability in aqueous solutions, data for intrinsic clearance (Clint = 48 mL/min/kg) and a half-life (t 1/2 = 12 min) showed decreased metabolic stability. As 5-FI.HCl showed both good absorption and ability to reach the systemic circulation of animals without the need to use vehicles containing cosolvents or surfactants, it was chosen to evaluate its effectiveness in the model of tuberculosis in mice. The in vivo results showed the concentration of the compound in plasma increasing within 30 min in the systemic circulation and the capacity of reducing the Mtb burden in the lungs at the concentration of 200 µmol/kg after 21 days of infection, with no toxicity in mice.

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.

Synthesis and Antimycobacterial Evaluation of N-(4-(Benzyloxy)benzyl)-4-aminoquinolines.

Tuberculosis remains a global health problem that affects millions of people around the world. Despite recent efforts in drug development, new alternatives are required. Herein, a series of 27 N-(4-(benzyloxy)benzyl)-4-aminoquinolines were synthesized and evaluated for their ability to inhibit the M. tuberculosis H37Rv strain. Two of these compounds exhibited minimal inhibitory concentrations (MICs) similar to the first-line drug isoniazid. In addition, these hit compounds were selective for the bacillus with no significant change in viability of Vero and HepG2 cells. Finally, chemical stability, permeability and metabolic stability were also evaluated. The obtained data show that the molecular hits can be optimized aiming at the development of drug candidates for tuberculosis treatment.

Synthesis and Antimycobacterial Activity of 3-Phenyl-1H-indoles.

Tuberculosis has been described as a global health crisis since the 1990s, with an estimated 1.4 million deaths in the last year. Herein, a series of 20 1H-indoles were synthesized and evaluated as in vitro inhibitors of Mycobacterium tuberculosis (Mtb) growth. Furthermore, the top hit compounds were active against multidrug-resistant strains, without cross-resistance with first-line drugs. Exposing HepG2 and Vero cells to the molecules for 72 h showed that one of the evaluated structures was devoid of apparent toxicity. In addition, this 3-phenyl-1H-indole showed no genotoxicity signals. Finally, time-kill and pharmacodynamic model analyses demonstrated that this compound has bactericidal activity at concentrations close to the Minimum Inhibitory Concentration, coupled with a strong time-dependent behavior. To the best of our knowledge, this study describes the activity of 3-phenyl-1H-indole against Mtb for the first time.

Handling the Hurdles on the Way to Anti-tuberculosis Drug Development.

The global epidemic of tuberculosis (TB) imposes a sustained epidemiologic vigilance and investments in research by governments. Mycobacterium tuberculosis, the main causative agent of TB in human beings, is a very successful pathogen, being the main cause of death in the population among infectious agents. In 2018, ~10 million individuals were contaminated with this bacillus and became ill with TB, and about 1.2 million succumbed to the disease. Most of the success of the M. tuberculosis to linger in the population comes from its ability to persist in an asymptomatic latent state into the host and, in fact, the majority of the individuals are unaware of being contaminated. Even though TB is a treatable disease and is curable in most cases, the treatment is lengthy and laborious. In addition, the rise of resistance to first-line anti-TB drugs elicits a response from TB research groups to discover new chemical entities, preferably with novel mechanisms of action. The pathway to find a new TB drug, however, is arduous and has many barriers that are difficult to overcome. Fortunately, several approaches are available today to be pursued by scientists interested in anti-TB drug development, which goes from massively testing chemical compounds against mycobacteria, to discovering new molecular targets by genetic manipulation. This review presents some difficulties found along the TB drug development process and illustrates different approaches that might be used to try to identify new molecules or targets that are able to impair M. tuberculosis survival.

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.

Organocatalytic access to enantioenriched dihydropyran phosphonates via an inverse-electron-demand hetero-Diels-Alder reaction.

The enantioselective inverse-electron-demand hetero-Diels-Alder reaction of the remote olefin functionality in dienamines has been developed by the simultaneous activation of α,ß-unsaturated aldehydes and acyl phosphonates. The dual activation is based on an organocatalyst that activates both the α,ß-unsaturated aldehyde, through dienamine formation, and the acyl phosphonate by hydrogen-bonding. The enantioselective reaction results in the formation of dihydropyran frameworks with three contiguous stereogenic centers. Different substitution patterns are possible for both the heterodiene and the dienophile, and the target products are obtained in good yields and up to 92% ee. The potential of the reaction is demonstrated by transformation of the products into valuable and complex synthons.