Design, Synthesis, Antimycobacterial Evaluation, and In Silico Studies of 3-(Phenylcarbamoyl)-pyrazine-2-carboxylic Acids

Phytochemical Content, Antibacterial Activity, and Antioxidant, Anti-Inflammatory, and Cytotoxic Effects of Traditional Medicinal Plants against Respiratory Tract Bacterial Pathogens

Respiratory tract infections (RTIs) are frequent ailments among humans and are a high burden on public health. This study aimed to determine the in vitro antibacterial, anti-inflammatory, and cytotoxic effects of indigenous medicinal plants used in the treatment of RTIs, namely, Senna petersiana, Gardenia volkensii, Acacia senegal, and Clerodendrum glabrum. Dried leaves were extracted using various organic solvents. Antibacterial activity was quantified using the microbroth dilution assay. Protein denaturation assays were used to evaluate anti-inflammatory activity. The cytotoxicity of the extracts towards THP-1 macrophages was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Antioxidant activity was determined using free radical scavenging activity and ferric-reducing power. Total polyphenolics were quantified. Liquid chromatography mass spectrometry was used to evaluate the acetone plant extracts. Nonpolar extracts had noteworthy antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Mycobacterium smegmatis where MIC values ranged between 0.16 and 0.63 mg/mL. At 100 μg/mL, A. senegal, G. volkensii, and S. petersiana had a nonsignificant effect on the viability of the THP-1 macrophages. The LC-MS analysis of the leaf extracts of S. petersiana detected Columnidin, Hercynine, L-Lysine citrate, and Gamma-Linolenate. A pentacyclic triterpenoid, cochalate, was detected in G. volkensii. Two flavonoids 7-hydroxy-2-(4-methoxyphenyl)-4-oxo-chroman-5-olate and (3R)-3-(2,4-dimethoxyphenyl)-7-hydroxy-4-oxo-chroman-5-olate were detected in the C. glabrum extract. The findings from this study indicated that the leaves of the selected plant extracts possess antioxidant, anti-inflammatory, and antibacterial activity. Therefore, they may serve as good candidates for further pharmaceutical investigations.

Synthesis, Biological Evaluation, and In Silico Modeling of N-Substituted Quinoxaline-2-Carboxamides

Despite the established treatment regimens, tuberculosis remains an alarming threat to public health according to WHO. Novel agents are needed to overcome the increasing rate of resistance and perhaps achieve eradication. As part of our long-term research on pyrazine derived compounds, we prepared a series of their ortho fused derivatives, N-phenyl- and N-benzyl quinoxaline-2-carboxamides, and evaluated their in vitro antimycobacterial activity. In vitro activity against Mycobacterium tuberculosis H37Ra (represented by minimum inhibitory concentration, MIC) ranged between 3.91–500 µg/mL, with most compounds having moderate to good activities (MIC < 15.625 µg/mL). The majority of the active compounds belonged to the N-benzyl group. In addition to antimycobacterial activity assessment, final compounds were screened for their in vitro cytotoxicity. N-(naphthalen-1-ylmethyl)quinoxaline-2-carboxamide (compound 29) was identified as a potential antineoplastic agent with selective cytotoxicity against hepatic (HepG2), ovarian (SK-OV-3), and prostate (PC-3) cancer cells lines. Molecular docking showed that human DNA topoisomerase and vascular endothelial growth factor receptor could be potential targets for 29.

A Microbiological, Toxicological, and Biochemical Study of the Effects of Fucoxanthin, a Marine Carotenoid, on Mycobacterium tuberculosis and the Enzymes Implicated in Its Cell Wall: A Link Between Mycobacterial Infection and Autoimmune Diseases

This study explored the antitubercular properties of fucoxanthin, a marine carotenoid, against clinical isolates of Mycobacterium tuberculosis (Mtb). Two vital enzymes involved in Mtb cell wall biosynthesis, UDP-galactopyranose mutase (UGM) and arylamine-N-acetyltransferase (TBNAT), were selected as drug targets to reveal the mechanism underlying the antitubercular effect of fucoxanthin. The obtained results showed that fucoxanthin showed a clear bacteriostatic action against the all Mtb strains tested, with minimum inhibitory concentrations (MIC) ranging from 2.8 to 4.1 µM, along with a good degree of selectivity index (ranging from 6.1 to 8.9) based on cellular toxicity evaluation compared with standard drug isoniazid (INH). The potent inhibitory actions of fucoxanthin and standard uridine-5’-diphosphate against UGM were recorded to be 98.2% and 99.2%, respectively. TBNAT was potently inactivated by fucoxanthin (half maximal inhibitory concentration (IC₅₀) = 4.8 µM; 99.1% inhibition) as compared to INH (IC₅₀ = 5.9 µM; 97.4% inhibition). Further, molecular docking approaches were achieved to endorse and rationalize the biological findings along with envisaging structure-activity relationships. Since the clinical evidence of the last decade has confirmed the correlation between bacterial infections and autoimmune diseases, in this study we have discussed the linkage between infection with Mtb and autoimmune diseases based on previous clinical observations and animal studies. In conclusion, we propose that fucoxanthin could demonstrate great therapeutic value for the treatment of tuberculosis by acting on multiple targets through a bacteriostatic effect as well as by inhibiting UGM and TBNAT. Such outcomes may lead to avoiding or decreasing the susceptibility to autoimmune diseases associated with Mtb infection in a genetically susceptible host.

Antimycobacterial, Enzyme Inhibition, and Molecular Interaction Studies of Psoromic Acid in Mycobacterium tuberculosis: Efficacy and Safety Investigations

The current study explores the antimycobacterial efficacy of lichen-derived psoromic acid (PA) against clinical strains of Mycobacterium tuberculosis (M.tb). Additionally, the inhibitory efficacy of PA against two critical enzymes associated with M.tb, namely, UDP-galactopyranose mutase (UGM) and arylamine-N-acetyltransferase (TBNAT), as drug targets for antituberculosis therapy were determined. PA showed a profound inhibitory effect towards all the M.tb strains tested, with minimum inhibitory concentrations (MICs) ranging between 3.2 and 4.1 µM, and selectivity indices (SIs) ranging between 18.3 and 23.4. On the other hand, the standard drug isoniazid (INH) displayed comparably high MIC values (varying from 5.4 to 5.8 µM) as well as low SI values (13.0–13.9). Interestingly, PA did not exhibit any cytotoxic effects on a human liver hepatocellular carcinoma cell line even at the highest concentration tested (75 µM). PA demonstrated remarkable suppressing propensity against UGM compared to standard uridine-5'-diphosphate (UDP), with 85.8 and 99.3% of inhibition, respectively. In addition, PA also exerted phenomenal inhibitory efficacy (half maximal inhibitory concentration (IC₅₀) value = 8.7 µM, and 77.4% inhibition) against TBNAT compared with standard INH (IC₅₀ value = 6.2 µM and 96.3% inhibition). Furthermore, in silico analysis validated the outcomes of in vitro assays, as the molecular interactions of PA with the active sites of UGM and TBNAT were unveiled using molecular docking and structure–activity relationship studies. Concomitantly, our findings present PA as an effective and safe natural drug plausible for use in controlling tuberculosis infections.

Ureidopyrazine Derivatives: Synthesis and Biological Evaluation as Anti-Infectives and Abiotic Elicitors

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) has become a frequently deadly infection due to increasing antimicrobial resistance. This serious issue has driven efforts worldwide to discover new drugs effective against Mtb. One research area is the synthesis and evaluation of pyrazinamide derivatives as potential anti-TB drugs. In this paper we report the synthesis and biological evaluations of a series of ureidopyrazines. Compounds were synthesized by reacting alkyl/aryl isocyanates with aminopyrazine or with propyl 5-aminopyrazine-2-carboxylate. Reactions were performed in pressurized vials using a CEM Discover microwave reactor with a focused field. Purity and chemical structures of products were assessed, and the final compounds were tested in vitro for their antimycobacterial, antibacterial, and antifungal activities. Propyl 5-(3-phenylureido)pyrazine-2-carboxylate (compound 4, MIC_Mtb = 1.56 μg/mL, 5.19 μM) and propyl 5-(3-(4-methoxyphenyl)ureido)pyrazine-2-carboxylate (compound 6, MIC_Mtb = 6.25 μg/mL, 18.91 μM) had high antimycobacterial activity against Mtb H37Rv with no in vitro cytotoxicity on HepG2 cell line. Therefore 4 and 6 are suitable for further structural modifications that might improve their biological activity and physicochemical properties. Based on the structural similarity to 1-(2-chloropyridin-4-yl)-3-phenylurea, a known plant growth regulator, two selected compounds were evaluated for similar activity as abiotic elicitors.