Shafi Ullah Khan

New one-pot synthesis of N-fused isoquinoline derivatives by palladium-catalyzed C–H arylation: potent inhibitors of nucleotide pyrophosphatase-1 and -3

Various N-fused isoquinoline derivatives were synthesized using a new one-pot reaction of 1-bromo-2-(2,2-difluorovinyl)benzenes with N-H group containing heterocycles followed by intramolecular palladium-catalyzed C-H arylation. The method described gives convenient access to diverse structures of N-fused polycyclic isoquinolines. Sixteen of the synthesized compounds were screened as potential human nucleotide pyrophosphatase/phosphodiesterase 1 and 3 (h-NPP-1 and h-NPP-3) inhibitors. The most effective h-NPP-1 inhibitor showed an IC50 value as high as 0.36 ± 0.06 μM, whereas the most potent h-NPP-3 inhibitor posessed an inhibitory value of 0.48 ± 0.01 μM. Kinetic and molecular docking studies of both most effective inhibitors were carried out.

Influence of the diversified structural variations at the imine functionality of 4-bromophenylacetic acid derived hydrazones on alkaline phosphatase inhibition: synthesis and molecular modelling studies

Alkaline phosphatase (AP) isozymes are present in a wide range of species from bacteria to humans with an ability to dephosphorylate and transphosphorylate a wide range of substrates. In humans, four AP isozymes have been identified such as tissue-nonspecific (TNAP), intestinal (IAP), placental (PLAP) and germ cell (GCAP) APs. Modulation of the activity of the different AP isozymes may have therapeutic implications in distinct diseases and cellular processes. To identify potent inhibitors of APs, a diverse range of 4-bromophenylacetic acid derived hydrazone derivatives has been synthesized and characterized by spectro-analytical methods and, in the case of 4i and 4q, by single crystal X-ray diffraction analysis. Among the tested series, several compounds were identified as lead candidates showing IC50 values from micro to nanomolar ranges. Compound 4k displayed exceptional activity with an IC50 value of 10 nM against h-IAP. This inhibitory effect is ∼10000-fold more potent than the standard drug L-phenylalanine. Compounds 4p, 4g and 4e were potent inhibitors of TNAP, PLAP and GCAP, respectively. Molecular docking studies of the respective potent inhibitors have been carried out to rationalize the important binding modes of the most active inhibitors.

Synthesis, computational studies and biological evaluation of new 1-acetyl-3-aryl thiourea derivatives as potent cholinesterase inhibitors

A new series of 1-acetyl-3-aryl thioureas (3f1–15) was synthesized by the reaction of acetyl isothiocyanate with a variety of suitably substituted aromatic anilines. The acetyl isothiocyanate was freshly prepared by reaction of corresonding acid chloride with potassium thiocyanate. The structural confirmation of all compounds was carried out by spectroscopic techniques and in case of 3a by X-ray diffraction study. The newly prepared compounds were subjected to computational studies and evaluated for their cholinesterase (acetylcholinesterase and butyrylcholinesterase) inhibition studies. Except 3f9 and 3f15, all the derivatives were found as selective inhibitor of acetylcholinesterase. Compound 3f2 (IC50 ± SEM = 1.99 ± 0.11 µM) was found to be the most potent inhibitor of acetylcholinesterase exhibited ≈11 times greater inhibitory potential than reference inhibitor i.e. neostigmine (IC50 ± SEM = 22.2 ± 3.2 µM). Compound 3f9 was found to be most potent butyrylcholinesterase inhibitor (IC50 ± SEM = 1.33 ± 0.11 µM), exhibiting ≈four times greater selectivity for butyrylcholinesterase over acetylcholinesterase. Molecular docking studies were carried out to determine the binding site interactions of these potent inhibitors with cholinesterases and also supported the experimental observations.

Synthesis, biological evaluation and docking studies of some novel isatin-3-hydrazonothiazolines

A new series of thirty nine 5-trifluoromethoxy/fluoro/chloro-isatin 3-hydrazonothiazolines 5a–n, 6a–o and 7a–j were synthesized by cyclization of the corresponding intermediate N4-aryl-substituted isatin-3-thiosemicarbazones 3 (prepared by condensation of appropriate isatin 1 with appropriate N4-aryl-substituted 3-thiosemicarbazides 2) with 4-chlorophenacyl bromide 4 in absolute ethanol or ethanol–benzene mixture and screened for their cytotoxicity, phytotoxicity, antifungal and urease inhibitory potential. All the synthesized compounds were found to be almost inactive in a brine shrimp (Artemia salina) bioassay, demonstrating IC50 values > 1.62 × 10−4 to 2.17 × 10−4 M. In a phytotoxicity assay, out of thirty-nine compounds tested, six i.e. 5i, 6h, 6i, 6k, 7c and 7h proved to be active, showing weak or non-significant (5–30%) activity at the highest tested concentration (500 μg mL−1). Similarly, in antifungal assay, twenty-six compounds i.e. 5a, 5b, 5d–f, 5h–j, 5m, 6a, 6b, 6d, 6j, 6l–o, 7a, 7b and 7d–j were found to be active against one, two, or three selected fungal strains, exhibiting weak or non-significant inhibition (10–30%). Of these, 6d and 6o displayed a relatively better activity profile in terms of the number of organisms inhibited. On the other hand, in a urease inhibition bioassay, all the synthesized hydrazonothiazolines proved to be potent enzyme inhibitors, demonstrating inhibitory activity with IC50 values ranging from 3.70 ± 0.62 to 849 ± 2.26 μM. Compounds 5c, 5g–i, 5k, 5n, 6b, 6c, 6i, 6k, 6l, 6n, 6o, 7a, 7e, 7i and 7j were, however, found to be relatively very potent, displaying outstanding enzymatic activity (IC50 = 3.70 ± 0.62 to 20.9 ± 0.57 μM), even better than the reference inhibitor thiourea (IC50 = 22.3 ± 1.12 μM), and may thus act as valid leads for further studies. Molecular docking studies of the synthesized isatin–thiazolines 5a–n, 6a–o and 7a–j were also carried out to elucidate their relationship with the binding pockets of the enzyme. This study offers the first example of exhibition of urease inhibitory potential by isatin–thiazolines and as such provides a solid basis for further research on these compounds to develop more potent antiurease compounds of medicinal/agricultural interest.

Synthesis of 2-arylated thiadiazolopyrimidones by Suzuki–Miyaura cross-coupling: a new class of nucleotide pyrophosphatase (NPPs) inhibitors

Over expression of nucleotide pyrophosphatase (NPPs) activity is associated with chondrocalcinosis, osteoarthritis, type 2 diabetes, neurodegenerative diseases, allergies and cancer metastasis. The potential of NPPs inhibitors as therapeutic agents, and the scarceness of their structure–activity relationship, encouraged us to develop new NPP inhibitors. Specifically, 2-bromo-7-methyl-5-oxo-5H-1,3,4-thiadiazolopyrimidine and its corresponding 6-fluoro derivatives were synthesized via a Suzuki–Miyaura reaction. The cross-coupling reaction with different arylboronic acids gave desired coupling products in good to excellent yields and showed wide functional group tolerance. Furthermore, all compounds were investigated for their potential to inhibit two families of ecto-nucleotidases, i.e. nucleoside triphosphate diphosphohydrolases (NTPDase) and NPPs. Interestingly, our compounds were identified as selective inhibitors of NPPs. Among derivatives 5a–5i, compound 5i (IC50 ± SEM = 0.39 ± 0.01 μM) was found to be the most potent inhibitor of h-NPP1 and compound 5h (IC50 ± SEM = 1.02 ± 0.05 μM) was found to be the most potent inhibitor of h-NPP3. Similarly, for fluorinated thiadiazolopyrimidones, derivative 6e (IC50 ± SEM = 0.31 ± 0.01 μM) exhibited the best inhibition of NPP1 and it was found that this compound exhibited ≈28 fold improvement in inhibitory potential as compared with the reference control i.e. Suramin (IC50 ± SEM = 8.67 ± 1.3 μM). Moreover, homology modelling and molecular docking studies of both inhibitors were carried out to suggest the putative binding mode of inhibitors with the respective enzyme i.e. h-NPP1 and h-NPP3.

2-Substituted 7-trifluoromethyl-thiadiazolopyrimidones as alkaline phosphatase inhibitors. Synthesis, structure activity relationship and molecular docking study

Alkaline Phosphatases (APs) play a key role in maintaining a ratio of phosphate to inorganic pyrophosphate (Pi/PPi) and thus regulate extracellular matrix calcification during bone formation and growth. Among different isozymes of AP, aberrant increase in the level of tissue non-specific alkaline phosphatase (TNAP) is strongly associated with vascular calcification and end-stage renal diseases. In this context, we synthesized a novel series of fluorinated pyrimidone derivatives, i.e., 2-bromo-7-trifluoromethyl-5-oxo-5H-1,3,4-thiadiazolepyrimidones. The bromine functionality was further used for derivatisation by nucleophilic aromatic substitution using amines as nucleophiles as well as by Palladium catalysed Suzuki-Miyaura reactions. The synthesized derivatives were found potent but non-selective inhibitors of both isozymes of AP. Arylated thiadiazolopyrimidones exhibited stronger inhibitory activities than 2-amino-thiadiazolopyrimidones. The binding modes and possible interactions of the most active inhibitor within the active site of the enzyme were observed by molecular docking studies.

Chemoselective synthesis and biological evaluation of arylated 2-(Trifluoromethyl) quinolines as nucleotide pyrophosphatase (NPPs) inhibitors

A new approach to arylated 2-trifluoromethylquinolines based on novel regioselective Suzuki-Miyaura coupling reactions has been developed. Moreover, site-selective, chemo-selective amination reactions were performed. The new 2-trifluoromethylquinoline derivatives were tested as potential NPPs inhibitors and evaluated for their potential to inhibit two families of ecto-nucleotidases, i.e. NPPs and nucleoside triphosphate diphosphohydrolases (NTPDases). Several derivatives were active on a nanomolecular concentration. The results were validated based on docking studies to study the active binding site of the molecules.

Antidiabetic activities of chloroform fraction of Anthocleista vogelii Planch root bark in rats with diet- and alloxan-induced obesity-diabetes

ETHNOPHARMACOLOGICAL RELEVANCE Anthocleista vogelii Planch is a medicinal plant traditionally used in West Africa for the management and treatment of diabetes mellitus. AIM OF THE STUDY To determine the antidiabetic activities of chloroform fraction (CF) of Anthocleista vogelii Planch root bark in rats with diet- and alloxan-induced obesity-diabetes. MATERIALS AND METHODS Inhibitory activities of CF against α-amylase and α-glucosidase activities were determined in vitro. Three weeks old rats were fed with high-fat diet for 9 weeks to induce obesity prior to further induction of diabetes using alloxan (150 mg/kg body weight, i.p.). Blood glucose levels and body weight were measured every 7 days throughout the experiment. Glucose tolerance was assessed in normal and CF-treated rats on day 21. Terminal blood samples were collected from sacrificed animals for the measurement of serum insulin levels. Pancreases were excised from treated and untreated animals for histopathological examination. RESULTS LCMS/MS chromatographic profile of CF via positive and negative modes revealed 13 and 23 compounds respectively. Further analysis revealed quebrachitol (QCT), loganin, sweroside, oleoside 11-methyl ester and ferulic acid, which have been previously reported for their antidiabetic activities, as constituents of CF. CF inhibited activities of α-amylase (IC50 = 51.60 ± 0.92 µg/ml) and α-glucosidase (IC50 = 5.86 ± 0.97 µg/ml) in a dose-dependent manner. Treatment of animals with obesity-diabetes with 100 and 200 mg/kg CF significantly improved glucose tolerance (P < 0.001) and enhanced serum insulin levels (P < 0.05) compared to diabetic control rats. CONCLUSIONS Antidiabetic activities of CF might be mediated via inhibition of α-amylase and α-glucosidase activities, elevation of serum insulin concentration, and enhancement of insulin and leptin sensitivity in obesity-diabetes rats. This study further substantiates the traditional use of A. vogelii in the management and treatment of diabetes in Africa and encourages further studies to investigate its mechanism of action.

Synthesis, Characterization and Cholinesterase Inhibition Studies of New Arylidene Aminothiazolylethanone Derivatives

BACKGROUND Alzheimers disease is caused by the destruction or loss of cholinergic cells that produce or use ACh in the brain, thereby reducing the availability of enzyme to other cells. The major treatment strategy for AD is to decrease the level of cholinesterase in the brain. OBJECTIVE The aim of this study was to describe the effect of novel series of thiazole derivatives i.e. arylidene aminothiazolylethanones (3a-h) as cholinesterase inhibitors (CEIs). METHOD A novel series of thiazole derivatives i.e. arylidene aminothiazolylethanones (3a-h) was synthesized by treating 3-chloropentane-2,4-dione (1) with urea followed by reaction with suitably substituted benzaldehydes. Structural confirmation of all the synthesized compounds was carried out by spectroscopic techniques (FTIR, 1H and 13CNMR) and elemental analysis. Furthermore, these derivatives were subjected to biological evaluation as potential inhibitors of cholinesterases i.e. acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). RESULTS In all synthesized compounds except two compounds i.e. 3a and 3f, all compounds were identified as selective inhibitors of AChE. Compound 3a exhibited potent inhibitory values against AChE (IC50± SEM = 1.78±0.11 µM), exhibiting ≈7 times greater selectivity for AChE over BChE. Kinetics studies were performed to find out the mechanism of inhibition against respective enzyme. In addition, molecular docking studies of most potent inhibitors were also carried out to determine the binding interactions with AChE and BChE, respectively. CONCLUSION In this study, novel thiazole derivatives i.e. arylidene aminothiazolylethanones were successfully synthesized, characterized and further screened for threir potential as cholinesterase inhibitors. All compounds were found as potent selective inhibitors of AChE except two compounds which exhibited dual inhibitory activities but both of these compounds were highly selective toward AChE as compared to BChE.

In Silco Screening of Parkia biglobosa Fatty Acids as Inhibitors of Α-Glucosidase, Aldehyde Reductase (ALR1) and Aldose Reductase (ALR2) Enzymes

Diabetes mellitus is a world health problem with high mortality and morbidity due to the complications; as a result of increased level of glucose concentration. The search for new antidiabetic drugs from natural products has been on increase. Though discovery of drug is time consuming with numerous challenges, therefore, in silico screening is now being used for the preclinical search and development of drugs within limited time. In this study, fatty acids determined from P. biglobosa seeds were screened in silico via molecular docking against α-glucosidase, ALR1 and ALR2 enzymes linked to type 2 diabetes mellitus complications using AutoDock Vina. These enzymes play different roles in glucose metabolism and associated to diabetes complications development. The results obtained from the docking studies revealed that docked ligands (fatty acid) bind firmly to the enzymes with the binding energy in the range of -4.12 Kcal mol-1 to -13.61 Kcal mol-1. Inhibition constant obtained for α-glucosidase was in micromolar and nanomolar for both ALR1 and ALR2 enzymes. Docking analysis showed different orientations of the ligands inside the active pocket of the enzymes, of all the ligands, linoleic acid forms perfect orientation with different amino acid residues of all the enzymes via hydrogen bonding formation when compared to the rest of fatty acids.