Letters in Drug Design & Discovery - Volume 15, Issue 4, 2018

Background: MRSA is a gram positive pathogen resistant to methicillin and other betalactam antibiotics, including penicillin, oxacillin, and declooxacillin. Statistical data suggest that as many as 19,000 people per year die from MRSA in the USA. Methods: Prudent use of existing drugs, coupled with the development of new antibacterial agents has been suggested as a way to combat the public health burden, posed by MRSA. In this work, about 60 compounds of bis-indoles (diindolylmethanes and diindolylmethenes) were synthesized and screened as antibacterial agents against S. aureus and methicillin-resistant S. aureus (MRSA). The quantitative structure-activity relationships (QSAR) of the compounds were also carried out in this work. Results: Good numbers of the compounds appear to be good antibiotic candidates against MRSA. The modelled complexes of S. aureus pyruvate kinase (PK) and the active compounds indicate that these bis-indole candidates fit perfectly in the binding groove between two monomers of PK. The compounds are predicted to have H-bond and steric interactions with important amino acid residues. Conclusion: The current study may lead to discover a new prospective of anti-MRSA candidates.

Background: Plant diseases caused by plant pathogens are important constraints to agricultural production throughout the world and at least 10% of global food production is lost to plant diseases. In order to discover new fungicides and control the plant diseases, a series of novel 1,2,4- triazole thioether derivatives carrying a pyrimidine moiety were designed and synthesized. Methods: Thirteen novel 1,2,4-triazole thioether derivatives carrying a pyrimidine moiety were designed by splicing the active substructure and synthesized under microwave irradiation condition. Their structures were characterized by 1H-NMR, 13C-NMR, ESI-MS and elemental analysis, and their antifungal activities were evaluated using the mycelium growth rate test. Results: These compounds were screened for antifungal activity against Colletotrichum orbiculare, Botrytis cinerea and Rhizoctonia solani at 50 μg/mL. Some compounds showed moderate to good antifungal activities. Especially the inhibition rate of compound 7c against C. orbiculare and R. solani were 80% and 76% respectively. Conclusion: A practical synthetic route to 1,2,4-triazole thioether derivatives by using the microwave- assisted method is presented. This study suggests that the 1,2,4-triazole thioether derivatives exhibited moderate to good inhibition activity against C. orbiculare and R. solani at 50 μg/mL, and could be further developed as potential fungicides.

Background: Infectious pathogenic bacteria are the key virulence in our daily life. Especially diseases produced by multidrug resistant Staphylococcus aureus (MRSA) still contributing in morbidity and mortality in humans. Discovery of new and safer antibiotics is an upmost task in current medicinal research. Methods: By keeping in mind the considerable antimicrobial activities of coumarin scaffold, 3-substituted coumarin derivatives 1-24 were synthesized by Knoevenegel condensation reaction. Different aryl aldehydes were treated with β-keto esters in the presence of organic base piperidine. All synthetic compounds were characterized by different spectroscopic techniques such as EI-MS, HREI-MS, 1H-NMR, and 13C-NMR. Compounds were screened to check for their in vitro anti- MRSA (multidrug resistant Staphylococcus aureus) activity against different strains of bacteria such as MRSA-252, EMRSA-16, EMRSA-17 and local clinical isolate. Micro-plate alamar blue assay (MABA) was used for this activity. Oxacillin, streptomycin, clindamycin and vancomycin were used as standards. Results: Results were reported as percent inhibition at 20 μg/mL concentration. Amongst all four standard drugs, only vancomycin was showed 19%, 24%, 21% and 40% inhibitions in case of MRSA-252, EMRSA-16, EMRSA-17 and local clinical isolate, respectively, at 20 μg/mL concentration. Most of the synthetic compounds were showed a weak to good inhibition as compared to standard, vancomycin. Conclusion: Newly identified compounds may serve as lead for future research in order to get the more powerful antibacterial agents.

Background: Influenza is a common respiratory tract infection caused by RNA-virus of the family Orthomyxoviridae; influenza virus, causing variety of symptoms including fever, nasal secretions, cough, muscle pain and pneumonia. It is classified into three distinct types A, B & C. Many 1,3,4-thiadiazoles, 1,3,4-oxadiazoles and 1,2,4-triazoles have showed broad spectrum of biological activities. These heterocycles are considered lead for their high antiviral activity against wide range of viruses. Methods: Research and online content related to chemistry of anti-influenza agents have been reviewed, five schemes were applied to obtain the target compounds, then these compounds underwent in vitro anti-influenza screening. Results: Thirty novel compounds were in vitro screened against the highly pathogenic avian influenza H5N1 virus in MDCK cells. Amantadine was used as control drug. Six compounds showed excellent activity (79-100 % virus inhibition) namely 6c, 14b, 14c, 19b, 30b, 30e with 14c being the most active compound. Five compounds exhibited moderate inhibition (44-70%) namely 5c, 6b, 23a, 23b, 30c. Conclusion: From the previous results, we found that presence of the triazole ring decreased the antiviral activity. While compound 19b that contains benzimidazole nucleus showed excellent inhibition. Presence of the thiadiazole ring greatly affected the activity in different ways according to the substitution on the ring. Moving to the oxadiazole series 14a-c, 16, 28b,c and 30a-f, the change in substitutions greatly affected the antiviral activity. Presence of 4-tolyl or 4-chlorophenyl at position 5 of the oxadiazole greatly enhanced the activity in 14b,c.

Background: Combrestastatin A-4 (CA-4) is a potent anticneoplastic and antiangiogenesis natural substance isolated from Combretum caffrum. Over the past two decades, numerous derivatives of CA-4 have been discovered. However, none of these derivatives has reached the clinical stage. Thus, continuing effort is needed in developing CA-4 analogues with improved pharmacological properties. Methods: In this study, two series of thiazolidine-2,4-dione and 2-oxoindoline derivatives incorporating 3,4,5-trimethoxybenzyl scaffold were designed and synthesized as CA-4 analogues. Results: Numerous CA-4 analogues bearing thiazolidine-2,4-dione/2-oxoindoline have been synthesized. These compounds were evaluated against several human cancer cell lines. It was found that a series of 5/7-substituted-1-(3,4,5-trimethoxy)benzylindoline-2,3-diones (2a-g) exhibited significant cytotoxicity. Especially compound 2d bearing a 5-bromo substituent showed the best activity with IC50 values in sub-microgram/mL scale in four human cancer cell lines tested. This compound also exhibited potent tubulin polymerization inhibitory activity. A series of (Z)-5-arylidene- 3-(3,4,5-trimethoxybenzyl)thiazolidine-2,4-diones (6a-j), on the other hand, displayed only moderate cytotoxic activities with only compound 6a showing comparable cytotoxicity to 2d. Finally, in silico molecular modeling and drug-likeness profiling revealed that five compounds 2b, 2d, 2e, 3e and 6a bound to tubulin active binding sites with strong binding affinities. Conclusion: This study discovered some novel CA-4 analogues with cytotoxic potency and antitubulin activity acceptable to be further developed as effective anticancer drug candidates.

Background: Carcer is one of the most common diseases that endanger human health and even lives in the world today. As it reported, lung, breast and colon cancers are most common in the developing and under developed countries. Fortunately, several therapeutic regimes have been successfully approached for fighting cancer nowadays. Osimertinib (AZD9291), approved in 2015 by the FDA, as the third-generation inhibitors were designed to conquer the severe drug resistance for nonsmall-cell lung cancer. However, the emergence of new drug resistance of AZD9291 called for more potent new drugs. In order to design more potent new molecular entities, introduction of a new skeleton, such as 1,3-thiazole, to modified AZD9291 might gain better results. Herein, we reported the synthesis and biological evaluation of eighteen thiazole-2-carboxamide derivatives in this paper. Methods: All synthesized target compounds were evaluated for their growth inhibitory activity against two human tumor cell lines in vitro via using CCK-8 assay. Based on the in vitro potency in the assays, a lead compound was selected for in vivo studies of toxicity and chemotherapeutic efficacy. Results: The reported functionalized thiazole-2-carboxamide derivatives displayed potency against both of the two cell lines at low μM concentrations. Compound 6f displayed significant antiproliferative activity against both human lung cancer cell line and breast cancer cell line with IC50 values 0.48 μM and 3.66 μM, respectively. And compound 6f showed potent in vivo efficacy with tumor inhibition of 84.3% at a dosage of 10 mg/Kg. Conclusion: A series of novel thiazole-2-carboxamide derivatives were designed and synthesized. Several synthesized thiazole-2-carboxamide derivatives showed potent efficacy against both human lung cancer cell line and breast cancer cell line in vitro. And a lead compound 6f was proved to be well tolerated and potent in vivo efficacy compared to the positive control AZD9291.

Background: Epilepsy affects approximately 50 million people globally. It is generally characterized by periodic seizures of unpredictable nature, though a variety of anticonvulsant drugs are available but the major drawback is undesirable side effects. Here an effort is being made to utilise the beneficial effect of benzothiazoles and oxadiazoles as potent anticonvulsants and there is an anticipation of synergistic effect from the hybrid molecule. Methods: Here a series of new hybrid molecules containing oxadiazole and benzothiazole pharmacophore were synthesised using appropriate synthetic route and characterised by IR, 1H NMR, 13C NMR, mass and elemental analysis. The synthesised compounds were examined for their maximal electroshock seizure (MES) and subcutaneous pentylene tetrazole (Sc PTZ) induced seizure and neurotoxicity screens. Those found potent were also evaluated for their CNS depressant effect. Results: Among the compounds tested 4m N-(6-fluro-1,3-benzothiazol-2-yl)-2-{[5-(pyridin-4-yl)- 1,3,4-oxadiazol-2-yl]sulfanyl}acetamide and 4n N-(6-Chloro-1,3-benzothiazol-2-yl)-2-{[5-(pyridin- 4-yl)-1,3,4-oxadiazol-2-yl]sulfanyl} acetamide showed protection from seizures in both the animal models at dose level of 30 mg/kg after 0.5 hr and at 100 mg/kg after 4 hr period indicating that the compound is potent and long acting. These compounds also exhibited lesser CNS depression and neurotoxicity. Conclusion: Among the synthesized compounds 4m and 4n possessed significant anticonvulsant activity without any neurotoxicity and CNS depressant effects. Thus the hybrid benzothiazolyl acetamide derivatives containing oxadizole scaffold provided a new opportunity for possible modification and future exploitation to get the safer and effective anticvulsant agents.

Background: Eplilepsy is defined as one of the most common neurological diseases, which affects approximately 50 million people all over the word. Despite the development of several new antiseizure drugs, the treatment of epilepsy remains still inadequate, because generally, anticonvulsant drugs can cause serious side effects such as neurotoxicity, depression, and impaired memory function. It is therefore imperative to search for new, safer, and more effective drugs for epilepsy. Methods: All the synthesized compounds were evaluated their anticonvulsant activities by the Maximal electroshock seizure and chemical-induced seizures models. The neurotoxicity of the compounds was measured in mice by the rotarod test. Results: Twenty 5-substitued-[1,2,4]triazolo[4,3-a]quinoxalin-4(5H)-one derivatives were synthesized and evaluated for anticonvulsant activities. Compound 5d was the most potent with an ED50 value of 27.39 mg/kg and a PI of 24.99. It also protected against seizures induced by pentylenetetrazole and bicuculline. In addition, compound 5d exhibited an ED50 value of 76.1 mg/kg and a PI > 39.44 following oral administration. Conclusion: All the synthesized compounds were confirmed by IR, 1H-NMR, 13C-NMR, and Mass spectra. Compound 5-hexyl-[1,2,4]triazolo[4,3-a]quinoxalin-4(5H)-one (5d) was safer than the commercially available drugs carbamazepine by administration of i.p in MES test. It also protected against seizures induced by chemical substances. Compound 5d should be a potential oral agent for treatment of epilepsy.

Background: Alzheimer's Disease (AD) is a complicated neurodegenerative disorder with a multifaceted pathogenesis.AD, characterized by gradual memory loss, falling in language ability and other cognitive deterioration, and has been a prominent risk to ageing population. This means that there is an urgent need to find new lead compounds for controlling and fighting against (AD). In this way, a new thiophene-2-pyrazoline derivatives (A1-A5) and benzothiazole derivatives (A6-A13) have been synthesized to give beneficial compounds to controlling and battling against (AD). Results: Compounds A5 and A13 showed the most remarkable activity with an 18.53 μM and 15.26 μM IC50 values against AChE enzyme. In like manner, compound A4 was active with a 20.34 μM IC50 value against MAO-A. These active compounds are in fact non-toxic making them very attractive for additional future studies. Enzyme kinetic was analyzed and the Lineweaver-Burk plot reveals that compound A13 was typically mixed AChE inhibitors, which showed significant similarity to donepezil. In addition, the best docking pose was done by analyzing the docking pattern of the most active compound A13 which was very compatible with the gorge and in interaction with both CAS and PAS. Conclusion: The synthesis of new thiophene-2-pyrazoline and benzothiazole derivatives targeting AChE/(MAO-A)/(MAO-B) enzymes was described. The selection of enzyme-kinetic analysis, molecular docking and toxicity test was led to good understanding to the therapeutic potential for the active derivatives. Therefore, these compounds may be accepted as promising leads for future research efforts in fighting against AD.

Background: In this work, a wide spectrum of 5-aminomethylene barbituric/ thiobarbituric acid derivatives was synthesized and evaluated for their Jack bean urease inhibitory activity. Methods: Among the synthesized compounds, 5-cyclohexylaminomethylene barbituric acid (3a) showed the most potent activity (IC50 = 25.8 μM), 4 times more potent than hydroxyurea (IC50 = 100.0 μM) and a similar activity to thiourea (IC50 = 22.0 μM), both being as the reference drugs. Results and Conclusion: Also, results from docking studies were in good agreement with those obtained in in vitro assay.

Background: NSAIDs have been extensively used for the treatment of pain and inflammation. There are about 30 different NSAIDs available in market and about 80 percent of prescriptions throughout the world contains one or the other painkiller. Chronic use of these drugs has many side effects such as gastric ulceration and the COX-2 inhibitors suffer from major drawback of cardiac toxicity. The need for a potential and safe NSAIDs has always led to the development of newer, better and safer drug molecules. In this article design and development of tetrahydrocarbazole derivatives with very low ulcerative index is reported. Methods: Fifteen tetrahydrocarbazole derivatives were synthesized on the basis of structural homology to indomethacin. Compounds were synthesized and characterized on the basis of spectral data. These were studied for their analgesic, anti-inflammatory and ulcerogenic activities. These compounds were subjected to molecular docking studies for understanding the possible mechanism of action and target. Results: The designed compounds were synthesized successfully in good yield and purity without much efforts. All compounds were evaluated by in vitro and in vivo assay, molecular modelling studies and ulcerative index. One of the compound (3-Aminophenyl) (6-chloro-1,2,3,4-tetrahydro- 9H-carbazol-9-yl) methanone 13 was found to be highly active in the in vitro and in vivo assessment also it was found to be highly safe on ulcerogenic index compared to the standard drugs. Conclusion: Tetrahydrocarbazoles were found to be promising scaffolds which can be developed into safe and potential non-steroidal anti-inflammatory agents.