https://orcid.org/0000-0002-8678-6352
Figures
Abstract
A series of newer previously synthesized fluorinated chalcones and their 2-amino-pyridine-3-carbonitrile and 2-amino-4H-pyran-3-carbonitrile derivatives were screened for their in vitro antitubercular activity and in silico methods. Compound 40 (MIC~ 8 μM) was the most potent among all 60 compounds, whose potency is comparable with broad spectrum antibiotics like ciprofloxacin and streptomycin and three times more potent than pyrazinamide. Additionally, compound 40 was also less selective and hence non-toxic towards the human live cell lines-LO2 in its MTT assay. Compounds 30, 27, 50, 41, 51, and 60 have exhibited streptomycin like activity (MIC~16–18 μM). Fluorinated chalcones, pyridine and pyran derivatives were found to occupy prime position in thymidylate kinase enzymatic pockets in molecular docking studies. The molecule 40 being most potent had shown a binding energy of -9.67 Kcal/mol, while docking against thymidylate kinase, which was compared with its in vitro MIC value (~8 μM). These findings suggest that 2-aminopyridine-3-carbonitrile and 2-amino-4H-pyran-3-carbonitrile derivatives are prospective lead molecules for the development of novel antitubercular drugs.
Citation: Lagu SB, Yejella RP, Nissankararao S, Bhandare RR, Golla VS, Subrahmanya Lokesh BV, et al. (2022) Antitubercular activity assessment of fluorinated chalcones, 2-aminopyridine-3-carbonitrile and 2-amino-4H-pyran-3-carbonitrile derivatives: In vitro, molecular docking and in-silico drug likeliness studies. PLoS ONE 17(6): e0265068. https://doi.org/10.1371/journal.pone.0265068
Editor: Mohammad Shahid, Aligarh Muslim University, INDIA
Received: July 2, 2021; Accepted: February 22, 2022; Published: June 16, 2022
Copyright: © 2022 Lagu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper.
Funding: Our manuscript study did not receive any external funding, however partial funding towards article processing charges has been provided by Deanship of Graduate Studies and Research, Ajman University and the same has been included in the manuscript. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
TB is responsible for the death of 1.4 million patients and among them 14.86% (2,08,000) were associated with HIV. Mtb is an agile bacterium which can shift from active to latent stage and vice-versa. Additionally, Tuberculosis (TB) is caused by the bacteria Mycobacterium tuberculosis (Mtb), which has been a global concern since decades and big burden on the healthcare system till today. It is one of the top ten leading causes of death according to the World Health Organization (WHO) 2019 reports and pose multiple resistance from the immunological protection of the host [https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death]. These typical microbiological features of Mtb exhibit for long term therapy and even multi drug resistance (MDR) to the existing WHO treatment protocols. However, due to improved diagnosis and treatment, the incidence of deaths from tuberculosis has been reduced in recent years. It’s anticipated that 66 million were rescued from the death during the year 2000–2020 [https://www.who.int/news-room/fact-sheets/detail/tuberculosis]. Nevertheless, the increase in the incidence of MDR and extensively drug-resistant (XDR) Mtb variants may complicate and create new challenges to this progress. In recent reports comparison in 2018, the number of patients with MDR or rifampicin-resistant TB (RR-TB) has increased by 10% in 2019. India has been listed in the top countries list for RR-TB [1]. MDR-TB, XDR-TB and RR-TB are posing greater challenges in the current treatment tactics employed. This scenario made scientists to drive and emphasize the significance of new research findings and development of new antitubercular medicines to compliment and supplement the current treatment protocols [2].
Chalcones are open chain flavonoids and have received large attention due to their diverse biological activities and synthetic applications in the preparation of medicinally useful heterocyclic molecules [3, 4]. They possess valuable antimicrobial, anti-inflammatory, antitubercular and anticancer activities [5–9]. Among them, fluorinated chalcones (Fig 1) were reported with excellent antimycobacterial activities [10–12]. Pyridine and pyran are biologically useful heterocycles with excellent therapeutic utility. Both these scaffolds are distributed in many naturally derived compounds like alkaloids, flavonoids, glycosides etc. Pyridine derivatives were reported to possess sundry of activities like anticancer, antitubercular, antiviral, antimicrobial, anti-inflammatory, antihistaminic etc., [13–27] and this ring is also present in a large variety of drugs used for the treatment of different diseases [28]. Pyran derivatives have been reported to exhibit antibacterial, anticancer, antitubercular, antioxidant, and other properties [29–37]. Antitubercular medications such as isoniazid, ethionamide, and prothionamide use the pyridine scaffold, whereas aminoglycoside antitubercular medications such as streptomycin, kanamycin, and amikacin use the reduced version of the pyran ring, tetrahydropyran (Fig 1). In the recent past, different fluorinated chalcones, pyridine and pyran derivatives were identified as potential antitubercular lead compounds [38–40] (Fig 2).
Fluorine substituents would change the physicochemical properties of drug-like candidates and drugs, such as increased penetration through biological membranes and metabolic stability, lower clearance, pKa value, better binding characteristics and potency [41–44]. Due to its similar sizes, the pyridine ring is a typical bioisosteric scaffold for benzene, pyrrole, and oxazole. In addition, it is utilized to substitute amines and amides bioisosterically. Basicity, stability, reduced molecular size, and aromatic nature confer superior pharmacokinetic qualities and binding abilities to pyridine, making it suitable for use in the preparation of lead molecules [24, 45]. Pyran scaffold like many other heterocyclic rings, aid bioactive compounds in altering pharmacokinetic and pharmacodynamic properties that make it an important component of many pharmaceuticals [46, 47]. In our previous published studies, we reported the antibacterial and antifungal properties of fluorinated chalcones and their pyridine and pyran derivatives with promising activities [48, 49]. Motivated by the excellent antimicrobial activities, we intended to test the target compounds against Mycobacterium tuberculosis in order to identify potential lead molecules against tuberculosis infections. Hence, herein we report the antitubercular evaluation of fluorinated chalcones and their 2-amino-pyridine-3-carbonitrile and 2-amino-4H-pyran-3-carbonitrile derivatives by standard computational and biological methods.
Materials and methods
In vitro antitubercular study
The antimycobacterial activity of target compounds (1–60) were evaluated against Mycobacterium tuberculosis using MABA. Briefly, sterile deionized water (200 μL) was added to all outer perimeter wells of sterile 96 well plate to minimize evaporation of medium in the test wells during incubation. 100 μL of the Middlebrook 7H9 broth was further added and serial dilution of compounds were made directly on plate. The final drug concentrations obtained were 100 to 0.2 μg/mL. The plates were later covered and sealed with parafilm and incubated at 37°C for five days. After incubation, 25 μL of freshly prepared 1:1 mixture of Alamar Blue reagent and 10% tween 80 was added to the plate and incubated for 24 hrs. A blue color in the well was interpreted as no bacterial growth, and pink color was scored as growth. The MIC was defined as lowest drug concentration which prevented the color change from blue to pink [50, 51]. Additionally, cLogP of all the target compounds has been calculated using SwissADME software.
Molecular docking studies
The molecular docking studies on the crystallographic structure of Thymidylate Kinase (PDB ID: 1G3U) retrieved in protein data bank was performed using AUTODOCK 4.2 version [52]. The AUTODOCK TOOLS were utilized for preparing the protein for docking. The polar hydrogen’s, partial charges and Gastegier charges were added using these tools. The flexible torsion of the ligand was assigned to proteins; the Auto Grid tool was used to implement the auto grid file, different for each protein. The grid parameters were set for each run. The AutoDock was run for binding molecules for molecular docking into the crystallographic structure of 1G3U active site. The cube selected covers the protein only of the binding site. The docking log file for each run was used to generate top three binding affinities of each protein, based on the binding energy of compounds. The saved 3D molecular poses were visualized using Discovery Studio.
MTT assay
The most active antitubercular lead compound 40 was screened for its cytotoxicity by MTT assay against the human normal liver cell lines (LO2) to assess its selectivity and safety using the procedure described as per literature [48].
In silico drug likeliness prediction
SwissADME, a web tool was used to evaluate the properties of the most potent compounds 20, 37, 40, and 60, as well as the marketed antitubercular drugs Ciprofloxacin, Streptomycin, and Pyrazinamide, for their in-silico parameters such as GI absorption, Lipinski rule of five, and CYP2C19 and CYP2D6 inhibition, in order to meet the requirements of the drug-likeliness. (http://www.swissadme.ch/ (accessed on 28 June, 2021)) [53].
Results and discussion
Chemistry
The synthesis and characterization of compounds 1–60 has been published previously [48, 49]. Fig 3 depicts the synthesis of target compounds (1–60).
In vitro antitubercular activity
Synthesized compounds (1–60) were evaluated for their antitubercular activity against tubercular strain H37RV (Tables 1–3, refer to S1 File). As reference standards, ciprofloxacin (MIC~9 μM), pyrazinamide (MIC ~25 μM), and streptomycin (MIC~11 μM) were utilized. The synthesized compounds can be classified as trifluoromethyl/trifluoromethoxy containing chalcones (1–20); 2-amino-pyridine-3-carbonitrile (21–40) and 2-amino-4H-pyran-3-carbonitrile (41–60) derivatives. The phenyl ring (R"; Tables 1–3, refer to S1 File) was substituted with electron withdrawing groups at ortho, meta, para or ortho-meta positions (compounds 1–6, 11–16, 21–26, 31–36, 41–46, and 51–56). Various heterocycles such as thiophene, furan, pyrrole, and indole ring systems were considered to examine bioisosteric substitution of the phenyl ring (compounds 7–10, 17–20, 27–30, 37–40, 47–50 and 57–60). In case of trifluoromethyl and trifluoromethoxy chalcone series (1–20), the MICs ranged from 38–189 μM (Table 1, refer to S1 File). In trifluoromethyl substituted chalcone derivatives, substituting Cl (10) in the para position resulted in a MIC of 40 μM, whereas substituting Cl in the meta (2)/ortho-meta (3) position or using nitro group in the ortho (4), meta (5), or para (6) position did not improve antitubercular activity when compared to the reference standards. Compounds 10 and 20 had the best activity among the bioisosteres, with MIC values of 40 and 38 μM, respectively.
In case of trifluoromethyl and trifluoromethoxy substituted 2-amino-pyridine-3-carbonitrile series (21–40), the range of MICs values were obtained from 8–134 μM. Substituting electronegative group (Cl or NO2) at positions ortho or para was found to be favorable for activity (compounds 21, 31, 23, 33, 24, 34). However, the compounds bearing heteroaryl scaffold (27–30, 37–40) were more active than the compounds containing phenyl ring with electronwithdrawing groups. Among them, compound 40 containing indole scaffold was most potent with a better MIC value (8 μM). This compound 40 was found to have activity similar to ciprofloxacin and streptomycin but was 3-fold potent than pyrazinamide.
Wheras the trifluoromethyl and trifluoromethoxy substituted 2-amino-4H-pyran-3-carbonitrile series (41–60) were shown the variation of MIC values (16–161 μM). Substitution of the electro negative group (Cl or NO2) at ortho or para positions was found to be more favorable for activity with best activity observed for compounds 41 and 51 with MIC values 17 μM and 16 μM respectively. The lowest activity was detected for 2-pyrrolyl substituent (49 and 59) with MIC values of 151 μM and 144 μM, whereas the best activity was obtained for compounds 50 and 60 containing indole ring with MIC value of 16 μM among all other bioisosteres 47–50, 57–60. Compounds 50 and 60 were found to have activity greater than pyrazinamide but less than ciprofloxacin and streptomycin respectively. Overall, these results indicated cyanopyridines and cyanopyrans as promising lead molecules for the development of newer antitubercular agents. A summary of the antitubercular activities of synthesized compounds (1–60) is depicted in Fig 4 whereas the structure activity relationships is shown in Fig 5.
Molecular docking studies
Understanding the mechanism of action of the antitubercular activity of the newly synthesized compounds, molecular docking studies was carried to predict the binding energy of ligands within the binding site of target proteins (Tables 4–6, refer to S1 File, Fig 6). Compound 40 had shown high binding energy (-9.67 kcal/mol) which was correlated with evaluated MIC value of 8 μM. It was found to be too close to methotrexate -10.0287 kcal/mol. Compound 26 had binding energy of -7.97 kcal/mol which corresponded to a MIC value of 33 μM whereas the binding energies for compounds 50 and 60 were found to be -9.82 and -9.49 kcal/mol. We docked the synthesized compounds in the Isoniazid (INH) active site, considering the previously documented thymidylate kinase (TK) inhibitory action of structurally similar pyridine and pyran antimicrobial drugs, as well as isoniazid [50, 54]. TK protein was retrieved from the protein data bank (PDB ID: 1G3U) to validate and designate the target protein for the antibacterial activity of newly synthesized 2-aminopyridine-3-carbonitrile derivative and 2-amino-4H-pyran-3-carbonitrile derivative. The docking conformation of compound 40 suggests good interactions with the active site residues of this protein. The docking interactions of compound 40 clearly reveals the importance of 6-trifluoromethoxyphenyl-4-heteroaryl cyanopyridines in enhancing the antimycobacterial activity over 6-trifluoromethylphenyl-4-heteroaryl cyanopyridines/pyrans. This compound had shown both hydrophobic and hydrogen bonding interactions. For instance, nitrogen of the pyridine scaffold had shown hydrogen bonding with amino acid ASP9 and the amino group at the 2nd position of pyridine ring had additional hydrogen bonding with the amino acids ASP163, GLU166 and MG:300 which enhanced the binding of this compound. In addition, the indole moiety at position-4 had strong hydrophobic (pi-pi stacking) interactions with the amino acid PHE70. The halogen bonding of the trifluoromethoxy group located on the 4th position of the phenyl ring substituted at the position-6 of pyridine motif with ASP94 had further substantiated the binding and enhanced the activity (Fig 6). The other interactions for compound 40 with the protein active site are depicted in Table 7 (refer to S1 File). Hence, the docking studies are in line with the structure activity relationships of the in vitro antitubercular activity data.
Cytotoxicity assay
The compound 40 was estimated with an IC50 value of >70 μg/mL against the tested human normal liver cell line (LO2) in its in vitro MTT assay (Table 8, refer to S1 File). This result suggested that compound 40 being most potent has selective activity towards the Mycobacterium tuberculosis H37Rv strain over the human cells. Hence it is a safe analogue to process the molecule further to develop the novel antitubercular agent.
In silico drug likeliness studies
Using the web based Swiss ADME program, some parameters of compounds 20, 37, 40 and 60 were computed along with control standards such as Ciprofloxacin, Streptomycin and Pyrazinamide (Table 9, refer to S1 File). The GI absorption was low for compounds 37 and Streptomycin. Compounds 20, 60, Ciprofloxacin and Streptomycin were found to be P-Glycoprotein (PgP) substrates. No compounds and standards allowed Lipinski violations except Streptomycin. In case of CYP2D6 inhibition, all compounds fared well except for 20. Compounds 37, 40 and 60 were found to be CYP2C19 inhibitors. Among all the compounds, 40 fared better in terms of activity and SWISSADME properties compared to 20, 37 and 60. It was observed that 40 inhibited CYP2C19, but did not inhibit CYP2D6. However, it had a high GI absorption rate, did not function as a PgP substrate, and passed the Lipinski Rule of 5. As a result, compound 40 possesses good drug-like qualities and can be used as a new lead compound for additional in-vivo research.
Conclusions
In this present study, a novel series of chalcones, pyridine-3-carbonitrile, 4H-pyran-3-carbonitrile scaffolds were evaluated for their antitubercular activity using in-vitro and in-silico methods. The antitubercular activities of compounds 27, 30, 40, 41, 50, 51, 60 consisting indole and 2-chlorophenyl moiety were exhibited most potency among all compounds being studied. The docking experiments suggested that these compounds might also inhibit 1G3U, considering as promising drug candidates as novel antitubercular drugs. The highest potent compound 40 was selective active against Mycobacterium tuberculosis H37Rv strain compared to the normal human cells and demonstrated good drug-like qualities in the in silico ADME experiments. Compound 40 can be further examined for in vivo characterization. Future research may be extended and continued in the direction of the synthesis of novel analogues and their toxicity testing.
Acknowledgments
L.S.B & Y.R.P like to acknowledge University College of Pharmaceutical Sciences Andhra Pradesh, India for providing the lab facilities and chemicals for this work. R.R.B and A.B.S would like to thank the Dean’s office of College of Pharmacy and Health Sciences, Ajman University, UAE & Vignan Pharmacy College, Vadlamudi, Andhra Pradesh, India for their support.
References
- 1.
Global Tuberculosis Report 2020. World Health Organisation. 2020 October 15. [https://www.who.int/publications/i/item/9789240013131].
- 2. Chauhan A, Kumar M, Kumar A, Kanchan K (2021) Comprehensive review on mechanism of action, resistance and evolution of antimycobacterial drugs. Life Sci 119301. pmid:33675895
- 3. Yazdan KS, Sagar GV, Shaik BA (2015) Biological and synthetic potentiality of chalcones: A review. J Chem Pharm Res 7:829–842.
- 4. Zhuang C, Zhang W, Sheng C, Zhang W, Xing C, Miao Z (2017) Chalcone: A Privileged Structure in Medicinal Chemistry. Chem Rev 117:7762–7810. pmid:28488435
- 5. Vásquez-Martínez YA, Osorio ME, San Martín DA, Carvajal MA, Vergara AP, Sanchez E, et al. (2019) Antimicrobial, anti-inflammatory and antioxidant activities of polyoxygenated chalcones. J Braz Chem Soc 30:286–304.
- 6. Rashid UH, Xu Y, Ahmad N, Muhammad Y, Wang L (2019) Promising anti-inflammatory effects of chalcones via inhibition of cyclooxygenase, prostaglandin E2, inducible NO synthase and nuclear factor κb activities. Bioorg Chem 87:335–365. pmid:30921740
- 7. Shaik AB, Bhandare RR, Nissankararao S, Edis Z, Tangirala NR, Shahanaaz S, et al. (2020) Design, facile synthesis and characterization of dichloro substituted chalcones and dihydropyrazole derivatives for their antifungal, antitubercular and antiproliferative activities. Molecules 25:3188. pmid:32668655
- 8. Dandawate P, Ahmed K, Padhye S, Ahmad A, Biersack B (2021) Anticancer Active heterocyclic chalcones: recent developments. Anti-Cancer Agents Med Chem (Formerly Current Medicinal Chemistry-Anti-Cancer Agents) 21:558–566. pmid:32628595
- 9. Zhou W, Zhang W, Peng Y, Jiang ZH, Zhang L, Du Z (2020) Design, Synthesis and Anti-Tumor Activity of Novel Benzimidazole-Chalcone Hybrids as Non-Intercalative Topoisomerase II Catalytic Inhibitors. Molecules 25:3180. pmid:32664629
- 10. Burmaoglu S, Algul O, Gobek A, Aktas AD, Ulger M, Erturk BG, et al. (2017) Design of potent fluoro-substituted chalcones as antimicrobial agents. J Enzyme Inhib Med Chem 32:490–495. pmid:28118738
- 11. Basha AB, Lohitha SVK, Puttagunta SB, Shaik A, Supraja K, Sai HK (2019) Synthesis and screening of novel lipophilic diarylpropeones as prospective antitubercular, antibacterial and antifungal agents. Biointerface Res Appl Chem 9:3912–3918.
- 12. Kishor P, Ramana KV, Shaik AB (2017) Antitubercular evaluation of isoxazolyl chalcones. Res J Pharm Biol Chem Sci 8:730–735.
- 13. El-Naggar M, Almahli H, Ibrahim HS, Eldehna WM, Abdel-Aziz HA (2018) Pyridine-ureas as potential anticancer agents: synthesis and in vitro biological evaluation. Molecules 23:1459. pmid:29914120
- 14. Prachayasittikul S, Pingaew R, Worachartcheewan A, Sinthupoom N, Prachayasittikul V, Ruchirawat S, et al. (2017) Roles of pyridine and pyrimidine derivatives as privileged scaffolds in anticancer agents. Mini Rev Med Chem 17:869–901. pmid:27670581
- 15. Desai NC, Somani H, Trivedi A, Bhatt K, Nawale L, Khedkar VM, et al. (2016) Synthesis, biological evaluation and molecular docking study of some novel indole and pyridine based 1, 3, 4-oxadiazole derivatives as potential antitubercular agents. Bioorg Med Chem Lett 26:1776–1783. pmid:26920799
- 16. Wang H, Wang A, Gu J, Fu L, Lv K, Ma C, et al. (2019) Synthesis and antitubercular evaluation of reduced lipophilic imidazo [1, 2-a] pyridine-3-carboxamide derivatives. Eur J Med Chem 165:11–17. pmid:30654236
- 17. Patel H, Chaudhari K, Jain P, Surana S (2020) Synthesis and in vitro antitubercular activity of pyridine analouges against the resistant Mycobacterium tuberculosis. Bioorg Chem 102:104099. pmid:32711084
- 18. Abhale YK, Deshmukh KK, Sasane AV, Chavan AP, Mhaske PC (2016) Fused Heterocycles: Synthesis and Antitubercular Activity of Novel 6-Substituted-2-(4-methyl-2-substituted phenylthiazol-5-yl) H-imidazo [1, 2-a] pyridine. J Heterocycl Chem 53:229–233.
- 19. Giri RR, Lad HB, Bhila VG, Patel CV, Brahmbhatt DI (2015) Modified pyridine-substituted coumarins: a new class of antimicrobial and antitubercular agents. Synth Commun 45:363–375.
- 20. Li T, Zhang J, Pan J, Wu Z, Hu D, Song B (2017) Design, synthesis, and antiviral activities of 1, 5-benzothiazepine derivatives containing pyridine moiety. Eur J Med Chem 125, 657–662. pmid:27721151
- 21. Pu SY, Wouters R, Schor S, Rozenski J, Barouch-Bentov R, Prugar LI, et al. (2018) Optimization of isothiazolo [4, 3-b] pyridine-based inhibitors of cyclin G associated kinase (GAK) with broad-spectrum antiviral activity. J Med Chem 61:6178–6192. pmid:29953812
- 22. Ragab A, Fouad SA, Ali OAA, Ahmed EM, Ali AM, Askar AA, et al. (2021) Sulfaguanidine Hybrid with Some New Pyridine-2-One Derivatives: Design, Synthesis, and Antimicrobial Activity against Multidrug-Resistant Bacteria as Dual DNA Gyrase and DHFR Inhibitors. Antibiotics 10:162. pmid:33562582
- 23. Pitucha M, Karczmarzyk Z, Swatko-Ossor M, Wysocki W, Wos M, Chudzik K, et al. (2019) Synthesis, in vitro screening and docking studies of new thiosemicarbazide derivatives as antitubercular agents. Molecules 24:251. pmid:30641902
- 24. Karunanidhi A, Ghaznavi-Rad E, Jeevajothi Nathan J, Joseph N, Chigurupati S, Mohd Fauzi F, et al. (2019) Bioactive 2-(methyldithio) pyridine-3-carbonitrile from Persian shallot (allium stipitatum regel.) exerts broad-spectrum antimicrobial activity. Molecules 24:1003. pmid:30871159
- 25. Abdelgawad MA, Bakr RB, Azouz AA (2018) Novel pyrimidine-pyridine hybrids: synthesis, cyclooxygenase inhibition, anti-inflammatory activity and ulcerogenic liability. Bioorg Chem 77:339–348. pmid:29421710
- 26. Abdellatif KR, Abdelall EK, Fadaly WA, Kamel GM (2015) Synthesis, cyclooxygenase inhibition, and anti-inflammatory evaluation of novel diarylheterocycles with a central pyrazole, pyrazoline, or pyridine ring. Med Chem Res 24:2632–2644.
- 27. Stone EA, Cutrona KJ, Miller SJ (2020) Asymmetric Catalysis upon Helically Chiral Loratadine Analogues Unveils Enantiomer-Dependent Antihistamine Activity. JACS 142:12690–12698. pmid:32579347
- 28. Hamada Y. Role of pyridines in medicinal chemistry and design of BACE1 inhibitors possessing a pyridine scaffold. IntechOpen; 2018. pp. 9–24.
- 29. El-Sayed EH, Fadda AA (2018) Synthesis and antimicrobial activity of some novel bis polyfunctional pyridine, pyran, and thiazole derivatives. J Heterocycl Chem 55:2251–2260.
- 30. Safari F, Hosseini H, Bayat M, Ranjbar A (2019) Synthesis and evaluation of antimicrobial activity, cytotoxic and pro-apoptotic effects of novel spiro-4 H-pyran derivatives. RSC Adv 9:24843–24851. pmid:35528646
- 31. Kumar D, Sharma P, Singh H, Nepali K, Gupta GK, Jain SK, et al. (2017) The value of pyrans as anticancer scaffolds in medicinal chemistry. RSC Adv 7:36977–36999.
- 32. Ferraz da Costa DC, Pereira Rangel L, Martins-Dinis MMDDC, Ferretti GDDS, Ferreira VF, Silva JL (2020) Anticancer potential of resveratrol, β-lapachone and their analogues. Molecules. 25, 893. pmid:32085381
- 33. Moulkrere BR, Orena BS, Mori G, Saffon-Merceron N, Rodriguez F, Lherbet C, et al. (2018) Evaluation of heteroatom-rich derivatives as antitubercular agents with InhA inhibition properties. Med Chem Res 27:308–320.
- 34. Kunigoshi U (1960) Synthesis of dehydroacetic acid isonicotinyl hydrazone potassium salt. Its in vitro antitubercular effect on a strain of virulent human-type tubercle bacilli. Chemotherapy 8, 84–85.
- 35. Alluri KK, Reshma RS, Suraparaju R, Gottapu S, Sriram D (2018) Synthesis and evaluation of 4′, 5′-dihydrospiro [piperidine-4, 7′-thieno [2, 3-c] pyran] analogues against both active and dormant Mycobacterium tuberculosis. Bioorg Med Chem 26:1462–1469. pmid:29501415
- 36. Gurunanjappa P, Ningappa MB, Kariyappa AK (2016) Synthesis of pyrazole fused pyran analogues: Antimicrobial, antioxidant and molecular docking studies. Chem Data Collect 5:1–11.
- 37. Momo CHK, Mboussaah ADK, François Zambou N, Shaiq MA (2020) New pyran derivative with antioxidant and anticancer properties isolated from the probiotic Lactobacillus plantarum H24 strain. Nat Prod Res 1–9. pmid:33225751
- 38. Danac R, Mangalagiu II (2014) Antimycobacterial activity of nitrogen heterocycles derivatives: Bipyridine derivatives. Part III. Eur J Med Chem 74:664–670. pmid:24268596
- 39. Van Der Westhuyzen R, Winks S, Wilson CR, Boyle GA, Gessner RK, Soares De Melo C, et al. (2015) Pyrrolo[3,4-c]pyridine-1,3(2H)-diones: A novel antimycobacterial class targeting mycobacterial respiration. J Med Chem 58:9371–9381. pmid:26551248
- 40. Mahdavi SM, Habibi A, Dolati H, Shahcheragh SM, Sardari S, Azerang P (2018) Synthesis and Antimicrobial Evaluation of 4H-Pyrans and Schiff Bases Fused 4H-Pyran Derivatives as Inhibitors of Mycobacterium bovis (BCG). Iran J Pharm Res 17:1229–1239. pmid:30568683.
- 41. Poonam S, Andrew DW (2007) The role of fluorine in medicinal chemistry. J Enzyme Inhib Med Chem 22:527–540. pmid:18035820
- 42. Sophie P, Peter RM, Steve S, Veronique G (2008) Fluorine in Medicinal Chemistry. Chem Soc Rev 37:320–330. pmid:18197348
- 43. William KH (2008) The Many Roles for Fluorine in Medicinal Chemistry. J. Med. Chem. 51:4359–4369. pmid:18570365
- 44. Eric PG, Kyle JE, Matthew DH, David JD, Nicholas AM (2015) Applications of Fluorine in Medicinal Chemistry. J Med Chem 58:8315–8359. pmid:26200936
- 45.
Meanwell NA. The influence of bioisosteres in drug design: tactical applications to address developability problems. In Tactics in Contemporary Drug Design. Springer, Berlin, Heidelberg.2013. 283–381.
- 46. Kumar KA, Renuka N, Kumar GV, Lokeshwari DM (2015) Pyrans: Heterocycles of chemical and biological interest. J Chem Pharm Res 7:693–700.
- 47. Geen GR, Evans JM, Vong AK, Katritzky AR, Rees CW, Scriven EFV (1996) Pyrans and their benzo derivatives: applications. Comprehensive heterocyclic chemistry II. 5:469–500.
- 48. Lagu SB, Yejella RP, Bhandare RR, Shaik AB (2020) Design, synthesis, and antibacterial and antifungal activities of novel trifluoromethyl and trifluoromethoxy substituted chalcone derivatives. Pharmaceuticals 13:375. pmid:33182305
- 49. Lagu SB, Yejella RP (2020) Design, synthesis, and characterization of the some novel 2-amino-pyridine-3-carbonitrile and 2-amino-4h-pyran-3-carbonitrile derivatives against antimicrobial activity and antioxidant activity. Asian J Pharm Clin Res 13:125–134.
- 50. Babu LS, Shaik AB, Prasad YR (2019) Synthesis, antibacterial, antifungal, antitubercular activities and molecular docking studies of nitrophenyl derivatives. Int J Life Sci Pharm Res 9:54–64.
- 51. Kasetti AB, Singhvi I, Nagasuri R, Bhandare RR, Shaik AB (2021). Thiazole–Chalcone Hybrids as Prospective Antitubercular and Antiproliferative Agents: Design, Synthesis, Biological, Molecular Docking Studies and In Silico ADME Evaluation. Molecules 26:2847. pmid:34064806
- 52.
Protein Data Bank, http://www.rcsb.org/pdb.
- 53.
SwissADME. http://www.swissadme.ch/ (accessed on 28th June 2021 and 15th September 2021).
- 54. Van Calenbergh S (2006). Structure-aided design of inhibitors of Mycobacterium tuberculosis thymidylate kinase. Verhandelingen-Koninklijke Academie Voor Geneeskunde van Belgie 68:223–48. pmid:17214439