Quinoxaline-based membrane-targeting therapeutic material: Implications in rejuvenating antibiotic and curb MRSA invasion in an in vitro bone cell infection model

Manifestation of resistance in methicillin-resistant Staphylococcus aureus (MRSA) against multiple antibiotics demands an effective strategy to counter the menace of the pathogen. To address this challenge, the current study explores quinoxaline-based synthetic ligands as an adjuvant material to target MRSA in a combination therapy regimen. Amongst the tested ligands (C1-C4), only C2 was bactericidal against the MRSA strain S. aureus 4 s, with a minimum inhibitory concentration (MIC) of 32 μM. C2 displayed a membrane-directed activity and could effectively hinder MRSA biofilm formation. A quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that C2 downregulated expression of the regulator gene agrC and reduced the fold change in the expression of adhesin genes fnbA and cnbA in MRSA in a dose-dependent manner. C2 enabled a 4-fold reduction in the MIC of ciprofloxacin (CPX) and in presence of 10 μM C2 and 8.0 μM CPX, growth of MRSA was arrested. Furthermore, a combination of 10 μM C2 and 12 μM CPX could strongly inhibit MRSA biofilm formation and reduce biofilm metabolic activity. The minimum biofilm inhibitory concentration (MBIC) of CPX against S. aureus 4 s biofilm was reduced and a synergy resulted between C2 and CPX. In a combinatorial treatment regimen, C2 could prevent emergence of CPX resistance and arrest growth of MRSA till 360 generations. C2 could also be leveraged in combination treatment (12 μM CPX and 10 μM C2) to target MRSA in an in vitro bone cell infection model, wherein MRSA cell adhesion and invasion onto cultured MG-63 cells was only ~17 % and ~ 0.37 %, respectively. The combinatorial treatment regimen was also biocompatible as the viability of MG-63 cells was high (~ 91 %). Thus, C2 is a promising adjuvant material to counter antibiotic-refractory therapy and mitigate MRSA-mediated bone cell infection.

Quinoxaline: A chemical moiety with spectrum of interesting biological activities

Quinoxaline (C8H6N2), commonly called 1,4-diazanaphthalene, 1,4-benzodiazine, or benzopyrazine, is a very potent nitrogenous heterocyclic moiety consisting of a benzene ring fused with the pyrazine ring. A number of different methods for the synthesis of quinoxaline derivatives have been reported in the literature, but the most effective method, commonly used for the synthesis of quinoxaline analogues involves the condensation of substituted o-phenylenediamines with 1, 2- dicarbonyl compounds in the presence of different catalyst(s). The presence of different types of catalysts and their concentration affects the overall yield of the product. Quinoxaline not only plays an important role as an organic reaction intermediate but also has a wide spectrum of interesting biological activities viz. antibacterial, antifungal, anticancer, anti-inflammatory, antiviral, and antiprotozoal activity, etc. Some commercially available drug molecules containing quinoxaline moiety are echinomycin (as antibacterial, antineoplastic, and nucleic acid inhibitor), triostins (cyclic desipeptide as an antibacterial agent), dioxidine and mequindox (as antibacterial agents), carbadox (controlling swine dysentery), desoxycarbadox (as swine growth promoter) and panadipion (as hepatoprotective agent), etc. A large number of quinoxaline analogues possessing different biological activities and their synthetic procedures have been patented worldwide.

Quinoxaline Moiety: A Potential Scaffold against Mycobacterium tuberculosis

Background. The past decades have seen numerous efforts to develop new antitubercular agents. Currently, the available regimens are lengthy, only partially effective, and associated with high rates of adverse events. The challenge is therefore to develop new agents with faster and more efficient action. The versatile quinoxaline ring possesses a broad spectrum of pharmacological activities, ensuring considerable attention to it in the field of medicinal chemistry. Objectives. In continuation of our program on the pharmacological activity of quinoxaline derivatives, this review focuses on potential antimycobacterial activity of recent quinoxaline derivatives and discusses their structure-activity relationship for designing new analogs with improved activity. Methods. The review compiles recent studies published between January 2011 and April 2021. Results. The final total of 23 studies were examined. Conclusions. Data from studies of quinoxaline and quinoxaline 1,4-di-N-oxide derivatives highlight that specific derivatives show encouraging perspectives in the treatment of Mycobacterium tuberculosis and the recent growing interest for these scaffolds. These interesting results warrant further investigation, which may allow identification of novel antitubercular candidates based on this scaffold.

Exploring Azatidinone Moiety: An Insight into its Anti-tubercular Potency

TB is becoming a worldwide problem and it was declared since 1993 by the World Health Organization (WHO), a global health emergency. The current problem of tuberculosis therapy is the emergence of multi-drug resistant (MDR) strains, caused by the improper use of antibiotics in chemotherapy of TB patients. Azatidinones, a β-lactam cyclic amide with four atoms in a ring, has been considered as a magic moiety (wonder nucleus) which possesses almost all types of biological activities. This diversity in the biological response profile has attracted the attention of many researchers to explore this skeleton to its multiple potential against several activities. Present article is sincere attempt to review chemistry, method of synthesis of azatidinones and to study azatidinones synthesized in last few years which have shown potent antitubercular activity.

Insights into the crystal structure of two newly synthesized quinoxalines derivatives as potent inhibitor for c-Jun N-terminal kinases

Two new compounds namely, ethyl (2E)-3-(dimethylamino)-2-(3-methoxyquinoxalin-2-yl)propen-2-enoate (II) and ethyl 2-(3-oxo-4-(prop-2-yn-1-yl)-3,4-dihydroquinoxalin-2-yl)-3-phenylpropanoate (III) have been synthesized from ethyl 2-(oxo-3,4-dihydroquinoxalin-2-yl) acetate (I). The compounds were characterized using NMR (¹H and ¹³C), Fourier transform infrared and confirmed by single crystal X-ray diffraction studies. The quinoxaline portion of II is almost planar with the substituent containing the dimethylamino and carboxyethyl groups rotated well out of its mean plane. In the crystal, C-H···O and C-H···N hydrogen bonds as well as C-H···π(ring) interactions form chains having a U-shaped cross-section and running along the c-axis direction. Two sets of pair-wise C-H···O hydrogen bonds connect the chains into corrugated sheets. In III, the three substituents on the dihydroquinoxaline moiety are rotated well out of its mean plane. Three sets of C-H···O hydrogen bonds as well as C-H···π(ring) and π-π-stacking interactions form layers approximately parallel to [001]. These are associated along the c-axis direction by additional C-H···π(ring) interactions. Additionally, the Hirshfeld surface analyses showed that the H···H contact is the most important interaction for both II and III. In addition to this, molecular docking and dynamics studies were carried for these two compounds with the c-Jun N-terminal kinases (JNK1) molecule.Communicated by Ramaswamy H. Sarma.

2D QSAR Analysis of Substituted Quinoxalines for their Antitubercular and Antileptospiral Activities

BACKGROUND

The Quantitative structure activity relationship for thirty two novel substituted quinoxalines was performed for their antitubercular (Mycobacterium tuberculosis H37Rv) and antileptospiral (Leptospirainterrogans) activities. The quinoxalines were substituted with azetidinones, thiazolidinones and fluoroquinolones. Several compounds exhibited good activity against both the infections and they all possess fluoroquinolone moiety with the quinoxaline.

METHODS

The models developed showed good linear relationship (r2 = 0.71-0.88), with an internal predictive ability (q2> 0.61) and good external predictive ability (pred_r2>0.71). The compounds were separated into a training set on which regression was performed and a test set on which the predictive ability of the model was tested. Other statistical parameters including Ro2, Ro'2, k, k' and Z- score were in the acceptable range.

RESULTS AND CONCLUSION

The descriptors obtained explained the necessity of spatial orientation of atoms including branching and adjacency, presence of electronegative groups, balance between lipophilic elements and their binding strengths.

Persulfate-promoted oxidative C–N bond coupling of quinoxalinones andNH-sulfoximines

A simple approach for a direct sulfoximination of quinoxalinonesviaK₂S₂O₈-mediated oxidative coupling is reported.

QSAR, docking studies of 1,3-thiazinan-3-yl isonicotinamide derivatives for antitubercular activity

The enzyme - enoyl acyl carrier protein reductase (enoyl ACP reductase) is a validated target for antitubercular activity. Inhibition of this enzyme interferes with mycolic acid synthesis which is crucial for Mycobacterium tuberculosis cell growth. In the present work 2D and 3D quantitative structure activity relationship (QSAR) studies were carried out on a series of thiazinan-Isoniazid pharmacophore to design newer analogues. For 2D QSAR, the best statistical model was generated using SA-MLR method (r²=0.958, q²=0.922) while 3D QSAR model was derived using the SA KNN method (q²=0.8498). These studies could guide the topological, electrostatic, steric, hydrophobic substitutions around the nucleus based on which the NCEs were designed. Furthermore, molecular docking was performed to gauze the binding affinity of the designed analogues for enoyl ACP reductase enzyme. Amongst all the designed analogues the binding energies of SKS 01 and SKS 05 were found to be -5.267kcal/mol and -5.237kcal/mol respectively which was comparable with the binding energy of the standard Isoniazid (-6.254kcal/mol).

Copper-catalysed oxidative amination of quinoxalin-2(1H)-ones with aliphatic amines

A novel, efficient and practical method for copper-catalysed oxidative C-3 amination of quinoxalin-2(1H)-ones with primary or secondary amines as the nitrogen sources has been developed.

A Structure-Activity Relationship Study of Naphthoquinone Derivatives as Antitubercular Agents Using Molecular Modeling Techniques

Tuberculosis (TB) is one of the major causes of death worldwide. Mycobacterium tuberculosis, the leading causative agent of TB, is responsible for the morbidity and mortality of a large population worldwide. In view of above and as a part of our effort to develop new and potent anti-TB agents, a series of substituted naphthoquinone derivatives were subjected to molecular modeling using various feature selection methods. The statistically significant best 2D-QSAR model having correlation coefficient [Formula: see text] and cross-validated squared correlation coefficient [Formula: see text] with external predictive ability of [Formula: see text] was developed by SA-PLS, and group-based QSAR model having [Formula: see text] and [Formula: see text] with [Formula: see text] was developed by SA-PLS. Further analysis using three-dimensional QSAR technique identifies a suitable model obtained by SA-partial least square method leading to antitubercular activity prediction. k-nearest neighbor molecular field analysis was used to construct the best 3D-QSAR model using SA-PLS method, showing good correlative and predictive capabilities in terms of [Formula: see text] and [Formula: see text]. The pharmacophore analysis results obtained from this study show that the distance between the aromatic/hydrophobic and the naphthoquinone moiety sites to the aliphatic and acceptor groups should be connected with almost the same distance for significant antitubercular activity. The information rendered by QSAR models may lead to a better understanding of structural requirements of antitubercular activity and also can help in the design of novel potent antitubercular activity.

A green approach toward quinoxalines and bis-quinoxalines and their biological evaluation against A431, human skin cancer cell lines

Background: The objective of this study was to develop a practical green procedure to synthesize quinoxalines and bis-quinoxalines and evaluate their inhibitory effects on the viability of A431 human epidermoid carcinoma cells. Method: A series of quinoxaline and bis-quinoxaline derivatives have been designed and synthesized following a microwave-assisted and bismuth nitrate-catalyzed eco-friendly route. A detailed comparison has been made between microwave-induced protocol with the reactions occurred at room temperature. The structure of the compounds have been elucidated by various spectroscopic methods and finally confirmed by x-ray crystallographic analyses. Results: Two quinoxaline derivatives, compounds 6 and 12 have demonstrated inhibitory effects on the viability of A431 human epidermoid carcinoma cells when compared with HaCaT nontumorigenic human keratinocyte cells. Conclusion: Notably, compound 6 inhibits Stat3 phosphorylation/activation in A431 skin cancer cells.