Novel heterocyclic 1,3,4-oxadiazole derivatives of fluoroquinolones as a potent antibacterial agent: Synthesis and computational molecular modeling.

Design and synthesis of novel series of 1,3,4-oxadiazoles containing FQs derivatives and screened their antibacterial, antimycobacterial properties. The synthesized compounds were characterized by different spectral techniques like IR, 1H NMR, 13C NMR, mass and elemental analysis. The results of the antimicrobial activity and compounds 6d, 6b, 6e, 6f and 6a demonstrated potent antibacterial activities with zone of inhibition of 42, 36, 37, 34 and 30 mm against S. aureus, E. faecalis, S. pneumoniae, E. coli and K. pneumoniae, respectively. 1,3,4-Oxadiazole derivatives 6a, 6b, 6 g were showed excellent antimycobacterial activity against M. smegmatis H37Rv with MICs 22.35, 16.20, 20.28 µg/mL, respectively. FQs 6d and 6b exhibited highest hydrogen bonding interactions with Asp83 (3.11 A˚), Ser80 (2.15 A˚) Asp27 (σ-σ), Arg87 (Π-Π), Arg87 (Π-Π), Ser80 (σ-σ), Ala84 (σ-σ) and binding energies ΔG = - 6.41, - 6.97 kcal/mol with active site of topoisomerase-IV from S. pneumoniae [4KPE]. We performed a computational investigation of compounds 6a-j for their absorption, distribution, metabolism and excretion (ADME) properties by using the Molinspiration, Molsoft toolkits. The ligands 6f, 6d and 6b reveal the highest pharmacokinetic properties and possess maximum drug-likeness model score 1.59, 1.46 and 1.23, respectively.

Hunig's base catalyzed synthesis of new 1-(2,3-dihydro-1H-inden-1-yl)-3-aryl urea/thiourea derivatives as potent antioxidants and 2HCK enzyme growth inhibitors.

A series of 1-(2,3-dihydro-1H-indan-1-yl)-3-aryl urea/thiourea derivatives (4a-j) have been synthesized from the reaction of 2,3-dihydro-1H-inden-1-amine (2) with various aryl isocyanates/isothiocyanates (3a-j) by using N,N-DIPEA base (Hunig's base) catalyst in THF at reflux conditions. All of them are structurally confirmed by spectral (IR, 1H &13C NMR and MASS) and elemental analysis and screened for their in-vitro antioxidant activity against DPPH and NO free radicals and found that compounds 4b, 4i, 4h &4g are potential antioxidants. The obtained in vitro results were compared with the molecular docking, ADMET, QSAR and bioactivity study results performed for them and identified that the recorded in silico binding affinities were observed in good correlation with the in vitro antioxidant results. The Molecular docking analysis had unveiled the strong hydrogen bonding interactions of synthesized ligands with ARG 160 residue of protein tyrosine kinase (2HCK) enzyme and plays an effective role in its inhibition. Toxicology studies have assessed the potential risks of 4a-j and inferred that all of them were in the limits of potential drugs. The conformational analysis of 4a-j inferred that the urea/thiourea spacer linking 2,3-dihydro-1H-inden-1-amino and substituted aryl units has facilitated all these molecules to effectively bind with ARG 160 amino acid residue present on the α-helix of the protein tyrosine kinase (2HCK) enzyme specifically on chain A of hemopoetic cell kinase. Collectively this study has established a relationship between the antioxidant potentiality and ligands binding with ARG 160 amino acid residue of chain A of 2HCK enzyme to inhibit its growth as well as proliferation of reactive oxygen species in vivo.

Multiple molecular targets mediated antioxidant activity, molecular docking, ADMET, QSAR and bioactivity studies of halo substituted urea derivatives of α-Methyl-l-DOPA.

A series of novel α-methyl-l-DOPA urea derivatives viz., 3-(3,4-dihydroxyphenyl)-2-methyl-2-(3-halo/trifluoromethyl substituted phenyl ureido)propanoic acids (6a-e) have been synthesized from the reaction of α-methyl-l-DOPA (3) with various aryl isocyanates (4a-e) by using triethylamine (5, TEA) as a base catalyst in THF at reflux conditions. The synthesized compounds are structurally characterized by spectral (IR, 1H &13C NMR and MASS) and elemental analysis studies and screened for their in-vitro antioxidant activity against DPPH, NO and H2O2 free radical scavenging assays and identified compounds 6c &6d as potential antioxidants. The acquired in vitro results were correlated with the results of molecular docking, ADMET, QSAR and bioactivity studies performed for them and predicted that the recorded in silico binding affinities are in good correlation with the in vitro antioxidant activity results. The molecular docking analysis has comprehended the strong hydrogen bonding interactions of 6a-e with 1CB4, 1N8Q, 3MNG, 1OG5, 1DNU, 3NRZ, 2CDU, 1HD2 and 2HCK proteins of their respective SOD, LO, PRXS5, CP450, MP, XO, NO, PRY5 and HCK enzymes. This has sustained the effective binding of 6a-e and resulted in functional inhibition of selective aminoacid residues to be pronounced as multiple molecular targets mediated antioxidant potent compounds. In addition, the evaluated toxicology risks of 6a-e are identified with in the potential limits of drug candidates. The conformational analysis of 6c & 6d prominently infers that urea moiety uniting α-methyl-l-DOPA with halo substituted aryl units into a distinctive orientation to comply good structure-activity to inhibit the proliferation of reactive oxygen species in vivo.

Synthesis and α-glucosidase inhibition activity of dihydroxy pyrrolidines.

A new series of Deacetylsarmentamide A and B derivatives, amides and sulfonamides of 3,4-dihydroxypyrrolidines as α-glucosidase inhibitors were designed and synthesized. The biological screening test against α-glucosidase showed that some of these compounds have the positive inhibitory activity against α-glucosidase. Saturated aliphatic amides were more potent than the olefinic amides. Among all the compounds, 5o/6o having polar -NH2 group, 10f/11f having polar -OH group on phenyl ring displayed 3-4-fold more potent than the standard drugs. Acarbose, Voglibose and Miglitol were used as standard references. The promising compounds 6i, 5o, 6o, 10a, 11a, 10f and 11f have been identified. Molecular docking simulations were done for compounds to identify important binding modes responsible for inhibition activity of α-glucosidase.

Synthesis, molecular properties prediction and anticancer, antioxidant evaluation of new edaravone derivatives.

A series of new edaravone derivatives 3-7 have been synthesized, characterised using various spectroscopic techniques and screened for their in vitro anti-cancer, antioxidant activities. Structure of 5d was further substantiated through single crystal X-ray diffraction. Among the tested, 5l exhibited pronounced activity against PC3 cancer cells. Compounds 5i, 5l, 7c showed potent activity against A549 cancer cells. Products 5k, 6, 7c demonstrated good antioxidant activity with MIC values of 18.60, 16.27, 16.07µg/mL respectively. Further the reported analogues were also tested on normal HEK293T cells and displayed low to good safer profiles. Derivatives 5l and 7c have come out to be safer potent anticancer, antioxidant agents. Additionally, the target products were subjected to their molecular properties prediction and drug likeness by employing Molinspiration and Osiris property explorer toolkits. None of them violated Lipinski's boundaries classifying the title compounds as potential anticancer and antioxidant agents.

Synthesis, in vitro anticancer and antimycobacterial evaluation of new 5-(2,5-dimethoxyphenyl)-1,3,4-thiadiazole-2-amino derivatives.

A series of 2,5-disubstituted-1,3,4-thiadiazole derivatives 5a-5l, 7a-7e and 9 have been synthesised and screened for in vitro antimycobacterial activity against Mycobacterium smegmatis MC-155. In addition these compounds have also been screened for cytotoxic activity against cancer cell lines HT-29, MDA-MB-231 by MTT colorimetric assay. The compounds are well characterized by spectral analysis viz. (1)H NMR, (13)C NMR, FT-IR, mass and HRMS. Screening results indicate that compounds 5g, 7a possess good antitubercular activity with MIC value 65.74 and 40.86, respectively, compounds 5g, 7a, 7b, 7d, 7e and 9 displayed promising cytotoxic activity against the cell lines tested. 5g and 7a stand out to be potent antimycobacterial and anticancer agents among the tested series. Further the title compounds were also tested on human normal cells HEK293T and are found to be safer with lesser cytotoxicity. It is interesting to observe that compound 5g has come out to be safer, potent anticancer and antimycobacterial agent.

Design, Synthesis and Biological Evaluation of Novel Heterocyclic Fluoroquinolone Citrate Conjugates as Potential Inhibitors of Topoisomerase IV: A Computational Molecular Modeling Study.

BACKGROUND & OBJECTIVE: A facile and efficient method for the synthesis of novel derivatives of FQ citrate conjugates with 1,2,4-triazoles and 1,3,4-oxadiazole scaffolds 8-11 using conventional, as well as microwave irradiation methods, was reported. Based on these original building blocks, the new derivatives of 3, 7-disubstituted fluoroquinolones bearing the oxadiazolyl-triazole groups were obtained. These invaluable derivatives are of great interest in medicinal and pharmaceutical studies because of their important biological properties. METHODS: All the reactions were examined under conventional as well as microwave mediated conditions. The structures of obtained compounds were confirmed by 1H NMR, 13C NMR, IR HRMS spectroscopy, and elemental analysis. The antibacterial and antifungal activities of these compounds were screened against Gram-positive, Gram-negative bacteria, and fungal stains by the agar well diffusion method. Cytotoxic assay of the title compounds was evaluated against cervical carcinoma cell line (HeLa) by using the MTT assay. The crystal structure of the Quinolone-DNA cleavage complex of type IV topoisomerase from S. pneumoniae (PDB ID: 3RAE) complex was obtained from the Protein Database (PDB, http:// www.rcsb.org). Molecular properties prediction-drug likeness was studied by Molinspiration and Molsoft software, while lipophilicity and solubility parameters were studied using the Osiris program. RESULTS: A novel approach for the synthesis of benzylthio-1,2,4-triazole and 1,3,4-oxadiazoles core with regioisomeric norfloxacin citrate conjugates was developed. Among the title compounds, 11b, 10a reveal pronounced activity against S. pneumoniae with minimum inhibitory concentrations of 0.89, 0.96 mg/mL and MBCs of 2.95, 2.80 mg/mL, respectively. Minimum Fungicidal Concentration (MFC) has been determined for each compound against two fungal strains. Compound 11b showed maximum anti-cancer activity against HeLa cell line with IC50 value 11.3 ± 0.41 comparable to standard drug DXN. For binding mode, active site residues and docking energies (ΔG =-7.9 Kcal/mol) for ligand 9b exhibited the highest hydrogen bonding (3.59274 A˚), Pi- Alkyl (5.14468 A˚) interactions with amino acid LEU479 of 3RAE protein. The compounds following the Lipinski 'Rule of five' were synthesized for antimicrobial and anti-cancer screening as oral bioavailable drugs/leads. Maximum drug likeness model score 1.52, 1.41 was found for compounds 10d, 11b. CONCLUSION: The present work, through simple synthetic approaches, led to the development of novel hybrids of fluoroquinolone containing citrate-triazole-oxadiazole pharmacophores that exhibited remarkable biological activities against different microorganisms and cell lines. The compounds showed suitable druglike properties and are expected to present good bioavailability profile. An efficient combination of molecular modeling and biological activity provided an insight into QSAR guidelines that could aid in further development and optimization of the norfloxacin derivatives.

A study on structural characterization of degradation products of cangrelor using LC/QTOF/MS/MS and NMR.

A complete degradation study was performed on cangrelor drug substance as per the ICH guidelines. The study reveals that a total of six degradation products (DP-1 to DP-6) were found and out of these, three unknown degradation products (DP-1, DP-5 and DP-6) were not reported in the literature. Based on the degradation study, the drug substance cangrelor was found to be sensitive towards acidic, basic and oxidative conditions. Besides, it was stable under thermal and photolytic stress conditions. The degradation products were characterized by using advanced LC/QTOF and MS/MS analysis. Further, the structures were characterized by NMR studies. The identified degradation products of cangrelor are valuable for cangrelor manufacturing process and quality control.

Development of a Simple, Highly Selective RP-LC Method for the Quantification of Diastereomers and Other Related Substances of Ezetimibe Using Multivariate Analysis.

A simple reverse phase method for the selective quantification of ezetimibe (EZM), its diastereomers and other related substances was developed. The method demonstrated an excellent separation between each of the 14 impurities (including diastereomers, specified impurities and degradation products) and EZM within a runtime of 45 min. The developed method was evaluated against the reported USP method, other literature methods found that none of them was able to separate/show the absence of all the diastereomers and degradation products. The critical method parameters were optimized using central composite design. Forced degradation studies proved the method to be highly specific and the structure of all the major degradation products were confirmed by LC-MS study. The results of validation proved the method to be precise (% RSD < 4), accurate (recoveries in range of 100 ± 6%), linear (R2 > 0.999) and sensitive (LOQ ≤ 0.04% and LOD ≤ 0.01%) for all the impurities and drug. The method is suitable for both drug substance and oral solid dosage form.

Molecular Modeling Studies of Novel Fluoroquinolone Molecules.

BACKGROUND: Fluoroquinolones have been the centre of considerable scientific and clinical interest due to their broad spectrum pharmacological activities. Pefloxacin is an analogue of norfloxacin, which is a 3rd generation of fluoroquinolone antibiotic similar to ciprofloxacin. Pefloxacin is used to treat a variety of bacterial infections like respiratory tract, ear, nose and throat (ENT) infections, skin infections, and urinary tract infections. Hydrazone as a pharmacophore unit that attracts the medicinal chemists because of structure activity relationship (SAR) studies of fluoroquinolones especially the functionality at C-3 position. Consequently, recognition and development of potential ligands specifically for a protein target forms the primary goal in drug discovery process. Among the different theoretical approaches available, Gold and Glide are the molecular docking methods which find application protein ligand studies. In the current study, the DNA gyrase of Staphylococcus aureus has been used as the target protein to understand their possible interactions. METHODS: The crystal structure of DNA gyrase (topoisomerase II) was downloaded from the Protein Data Bank (PDB ID: 2XCS, 3FOE) and molecular docking studies were performed using the docking programs like Gold 3.2 (Genetic Algorithm for Ligand Docking), Glide 5.0 (Grid Based Ligand Docking with Energetic). Melting points were uncorrected and determined in open capillary tubes in a melting point apparatus. TLC was performed on silica gel-G and spotting was done using iodine/ KMnO4 staining or UV-light. The following experimental procedures are representive of the general procedures used to synthesize all compounds. RESULTS: The docking experiments of the title compounds with 2.1 Å crystal structure of DNA gyrase 2XCS, 3FOE using Gold 3.2 and Glide 5.0 is carried out to understand the binding interactions of the novel ligands with the protein, contributing for antibacterial activity. The compounds in general exhibited good binding interactions like H-bonding interaction and π-π interactions which stabilize the protein-ligand complexes and responsible for good fitness scores in both the protocols. CONCLUSION: In summary, a new series of novel pefloxacin hydrazones 5a-5n were studied for their interactions with Staphylococcus aureus DNA gyrase protein by Glide 5.0 and Gold 3.2 molecular docking protocols [PDB IDS: 2XCS, 3FOE]. Among the tested molecules, compound 5g exhibited a good Glide score value of - 7.73 and Glide energy -51.24 with emodel value of -66.16. The nice docking scores of 5g, 5a, 8h, 5m and 5b revealed that these compounds are well accommodated on the active site residues of DNA gyrase enzyme. From the docking study, we have explored the probable binding mode and the binding pattern of compounds 5f, 5l, 5h, 5d, and 5n showed that they strongly interact with in the active site of Staphylococcus aureus of DNA gyrase enzyme. From screening results it is found that compounds having aromatic ring substituted with electron releasing groups are showing potent docking scores and exhibited better fitness than reference compounds CPF and CA4. An efficient combination of molecular modeling and biological activity provided an insight into QSAR guide lines that could aid in further development and optimization of the pefloxacin derivatives.

Novel degradation products of argatroban: Isolation, synthesis and extensive characterization using NMR and LC-PDA-MS/Q-TOF.

Forced degradation study of argatroban under conditions of hydrolysis (neutral, acidic and alkaline), oxidation, photolysis and thermal stress, as suggested in the ICH Q1A (R2), was accomplished. The drug showed significant degradation under hydrolysis (acidic, alkaline) and oxidation (peroxide stress) conditions. The drug remained stable under thermal and photolytic stress conditions. In total, seven novel degradation products (DP-1 to DP-7) were found under diverse conditions, which were not reported earlier. The chemical structures of these degradation products were characterized by 1H NMR, 13C NMR, 2D NMR, Q-TOF-MSn and IR spectral analysis and the proposed degradation products structures were further confirmed by the individual synthesis.

Design, Synthesis and Antibacterial Evaluation of Compounds Based on New Benzoxepine-oxime-1,2,3-triazole Hybrid.

BACKGROUND: A library of compounds related to the new benzoxepine-oxime-1,2,3-triazole hybrid was created as probable antibacterial agents. Their synthesis involved a Cu-catalyzed azidealkyne cycloaddition (CuAAC) as a key step to construct the desired 1,2,3-triazole ring. Thus the click reaction between the appropriate alkyne containing the benzoxepine-oxime framework with aryl azides afforded the target compounds in good yields. METHOD: To assess their antibacterial properties all the synthesized compounds were tested using four bacterial strains consisting of one Gram-positive and three Gram-negative species. RESULTS & CONCLUSION: These compounds were generally found to be effective towards gram -ve species and one of them showed selective cytotoxicity against lung cancer cell line.

Synthesis, molecular modeling and evaluation of α-glucosidase inhibition activity of 3,4-dihydroxy piperidines.

Biological evaluation of 3,4-dihydroxy piperidines as α-glucosidase inhibitors is being reported for the first time. Forty-five derivatives (amides, di-amides and sulfonamides) were made using cis and trans 3,4-dihydroxy piperidines to evaluate their α-glucosidase inhibition activity. Polar groups (-OH, -NH2) on phenyl ring having derivatives 5i, 5l, 7g, 7i &12j showed excellent activity compared to standard references. Acarbose, Voglibose and Miglitol were used as standard references. Molecular docking simulations were done for compounds to identify important binding modes responsible for inhibition activity of α-glucosidase.

User-Friendly HPLC Method Development and Validation for Determination of Enalapril Maleate and Its Impurities in Enalapril Tablets.

The official method for the determination of Enalapril Maleate and its related substances in European Pharmacopoeia (EP) is a gradient liquid chromatographic method. The method used styrene-divinylbenzene copolymer column, mobile phase buffer pH 6.8 and column oven temperature 70°C. In this method, the separation between main component Enalapril and Ph. Eur. Imp-A was not completed hence the achieving system suitability requirement is a tough task and it requires quite often adjustment in chromatographic parameters. Moreover, column oven temperature 70°C is not user friendly to HPLC instruments and users. In this study, several changes were introduced to the method in order to improve the separation, peak shapes and to overcome the column oven temperature. A new user-friendly stability-indicating RP-HPLC method was developed for Enalapril related substances analysis. The developed method uses a ZORBAX Eclipse XDB-C18 column with column oven temperature at 55°C and mobile phase containing acetonitrile and a phosphate buffer at pH 3.0. The method is capable of separating all the known impurities with resolution more than 3.5, which is much better than that obtained with the existing monograph methods. The optimized method was validated and demonstrated to have acceptable specificity, sensitivity, linearity, accuracy, precision, robustness, solution stability and equivalency to the EP method. The developed method proved to be applicable to a wide number of C18 reversed-phase columns. In addition, the Enalapril assay method also presented with 20 min run time.

Synthesis, molecular modeling and biological evaluation of aza-flavanones as α-glucosidase inhibitors.

An efficient acid catalyzed methodology has been employed to synthesize a variety of aza-flavanones and their α-glucosidase inhibitory activity is evaluated using acarbose, miglitol and voglibose as reference standards. Molecular modeling studies were performed for all compounds to identify the important binding modes responsible for the inhibition activity of α-glucosidase which helped find key interactions between the enzyme and the active compounds. Among all the compounds 5g, 5r and 5w have shown high α-glucosidase inhibition activity compared to standard reference drugs and have been identified as promising potential antidiabetic agents. This study is the first biological evaluation of aza-flavanones as α-glucosidase inhibitors.

Development and Validation of a New Stability-Indicating RP-UPLC Method for the Quantitative Determination of Bromfenac Sodium and Its Impurities in an Ophthalmic Dosage Form.

A new rapid stability-indicating reversed-phase UPLC method was developed and validated for the determination of Bromfenac sodium and its impurities in Bromfenac ophthalmic solution. During literature search, only a few publications were found about Bromfenac sodium. There is no official monograph in the pharmacopoeias about Bromfenac sodium. Chromatographic separation has been achieved on a polar-embedded Waters Acquity BEH Shield RP18 (100 mm × 2.1 mm, 1.7 µm) column under gradient elution by using a binary mixture of potassium dihydrogen phosphate (0.01 M, pH 3.3) and acetonitrile (ACN) at a flow rate of 0.5 mL/min. Chromatogram was monitored at 265 nm using a photodiode array detector (PDA). The drug and its related impurities are eluted within 13 min. Resolution of Bromfenac sodium and all eight potential impurities have been achieved greater than 4.0 for all pairs of compounds. To prove the stability-indicating power of the method, the drug was subjected to hydrolytic (acid, alkaline and water), oxidative, photolytic and thermal stress, and the major degradation products were identified based on LC-MS analysis. The developed method was validated as per ICH guidelines with respect to specificity, linearity, limit of detection, limit of quantification, precision, accuracy and robustness.

Development and Validation of a Novel Stability-Indicating RP-HPLC Method for the Simultaneous Determination of Related Substances of Ketoprofen and Omeprazole in Combined Capsule Dosage Form.

A novel, simple, sensitive, selective and reproducible stability-indicating high performance liquid chromatographic method was developed for the quantitative determination of degradation products and process-related impurities of ketoprofen (KET) and omeprazole (OMZ) in combined oral solid dosage form. Chromatographic separation was achieved on a Phenomenex Luna C18 (2) column (150 × 4.6 mm, 5 µm) under gradient elution by using a binary mixture of potassium dihydrogen phosphate buffer and acetonitrile at a flow rate of 0.8 mL/min. Chromatogram was monitored at 233 nm for KET impurities and at 305 nm for OMZ impurities using a dual wavelength UV detector. Resolution for KET and OMZ and 14 impurities was found to be >1.5 for any pair of components. Typical retention behaviors of impurities at various pH values were depicted graphically. To prove the stability-indicating power of the method, the drug product was subjected to hydrolytic, oxidative, photolytic, humidity and thermal stress conditions as per ICH. The developed method was validated according to the current ICH guidelines for specificity, limit of detection, limit of quantification, linearity, accuracy, precision, ruggedness and robustness.

Development and validation of a simple, sensitive, selective and stability-indicating RP-UPLC method for the quantitative determination of ritonavir and its related compounds.

A simple, sensitive, selective and reproducible stability-indicating ultra-performance liquid chromatographic method was developed for the quantitative determination of degradation products and process-related impurities of Ritonavir in a pharmaceutical dosage form. Chromatographic separation was achieved on a polar embedded Waters Acquity BEH Shield RP18 (100 × 2.1 mm, 1.7 µm) column thermostated at 50°C under gradient elution by using a binary mixture of potassium dihydrogen phosphate (0.01 M, pH 3.5) and acetonitrile at a flow rate of 0.5 mL/min. Chromatogram was monitored at 240 nm using a photodiode array detector. The drug and its related impurities are eluted within 20 min. To prove the stability-indicating power of the method, the drug was subjected to hydrolytic (acid, alkaline and water), oxidative, photolytic and thermal stress conditions. The unknown degradants were identified by the LC-MS-MS method, which revealed protonated molecular ion peaks [M + H](+) at m/z 551.40 for hydrolytic degradants, and m/z 737.60 and m/z 753.40 for photolytic degradants. A plausible mechanism for the formation of degradation and process impurities was proposed. The performance of the method was validated according to the International Conference on Harmonization guidelines.