Publications
Advancement in the sulfone-based dendrimers: From synthesis to application
Shaziya Khanam, Sunil K. Rai, Ashish K. Tewari*
Adv. Mater. Lett 2017, 8, 1005-1019
The development of sulfone-based macromolecules (polymer to dendrimers) has been inspired and prompted by much interesting importance of sulfone chemistry. Literature reveals that dendrimers are more demanding than the polymer in many aspects, because of its unique structural properties. Inspite of increasing importance and applications of dendrimers, it has a lot of hindrance regarding the tedious way of synthesis, which requires large excess of reagent and several problems in isolation. Therefore, time to time several tactics of synthesis has been developed. It was also well known that sulfonylation reaction is not only fast and easy to handle but also aryl sulfonylchloride derivatives are inexpensively available. Nowadays, sulfone-based dendrimers are exponentially expanding its application in disciplines of science which lie in organic synthesis, material sciences, combinatorial chemistry, medicinal chemistry and chemical biology. In this review, we have compiled the types of dendrimer and chiefly focused on the synthesis of sulfone-based dendrimers and their applications, in short. Further, future prospect of sulfone-based dendrimers in various branches of science has been outlined.
An efficient and controlled synthesis of persulfonylated G1 dendrimers via click reaction
Shaziya Khanam, Sunil K. Rai, Deepshikha Verma, Ranjana S. Khanna and Ashish K. Tewari*
RSC Adv., 2016,6, 56952-56962
This work presents the first report, we believe, on controlled synthesis of clickable dendrimers using aromatic and heteroaromatic cores and persulfonylated dendrons. Owing to poor thermal stability of persulfonylated dendrons, CuAAC reaction conditions were standardized at room temperature. Click reactions went smoothly with Cu(PPh3)3Br complex in the presence of tridentate chelating ligands and produced copper-free G1 dendrimers in excellent yield. This methodology has now unveiled the peripheral decoration of high generation POPAM dendrimers with persulfonyl groups in a one-step click reaction.
Polymorphic study and anti-inflammatory activity of a 3-cyano-2-pyridone based flexible model
Sunil K. Rai, Praveen Singh, Shaziya Khanam and Ashish K. Tewari*
New J. Chem., 2016,40, 5577-5587
This work deals with the synthesis, crystallization and the polymorphic interpretation of 2-{3-[3-cyano-6-methyl-2-oxo-4-phenylpyridin-1(2H)-yl]propoxy}-4-methyl-6-phenylnicotinonitrile (2). The quantitative analysis of the two polymorphs has been achieved through single crystal X-ray diffraction and Hirshfeld surface analysis. However, differential scanning calorimetry has been performed to determine the thermal stability and density functional theory to interpret the conformation on the propylene linker. Furthermore, the binding affinity of compound 2 was evaluated through a docking study in the COX-2 active site. An in vivo study revealed significant anti-inflammatory activity. Moreover, solubility of both polymorphs was checked in a 50% MeOH–water mixture and phosphate buffer (pH = 7.40).
Experimental and Theoretical Study for the Assessment of the Conformational Stability of Polymethylene-Bridged Heteroaromatic Dimers: A Case of Unprecedented Folding
Sunil K. Rai, Praveen Singh, Ranjeet Kumar, Ashish K. Tewari*, Jiří Hostaš, Ramachandran Gnanasekaran, and Pavel Hobza*
Cryst. Growth Des. 2016, 16, 3, 1176–1180
This is the first report on the folding phenomenon of pyridazinone and triazinone dimers (1–5) bridged through an alkyl chain. Among them, direct evidence of conformational preference of 1, 2, and 5 was obtained through single crystal X-ray structures. However, prevalence of folded conformations was analyzed through theoretical investigation.
Design and Synthesis of 2-Pyridone Based Flexible Dimers and Their Conformational Study through X-ray Diffraction and Density Functional Theory: Perspective of Cyclooxygenase-2 Inhibition
Sunil K. Rai, Shaziya Khanam, Ranjana S. Khanna, and Ashish K. Tewari*
Cryst. Growth Des. 2015, 15, 3, 1430–1439
This paper describes the results of X-ray crystallography of 4-methyl-2-oxo-6-phenyl-1,2-dihydropyridine-3-carbonitrile (1) and its propylene bridged dimers 2 and 3. Influence of inter- and intramolecular interactions on the conformation of propylene linker have been studied through single crystal X-ray crystallography and density functional theory studies. Hirshfeld surface analysis has been employed for the study of intermolecular interactions. However, differential scanning calorimetry analysis of compounds 2 and 3, and thermogravimetric analysis of compound 3 has been performed to determine the thermal stability. Along with molecular packing and thermal analysis, molecular docking has also been performed in the catalytic site of cyclooxygenase-2 to identify the potential anti-inflammatory activity of dimer 2 and 3. The above results suggest that the supramolecular aggregate structures which are formed in solution are of lowest energy. However, cyclooxygenase-2 active site prefers the higher energy conformers.
Unusual reverse face-to-face stacking in propylene linked pyrazole system: perspective of organic materials
Sunil Kumar Rai, Priyanka Srivastava, Hariom Gupta, Maria del C. Puerta, Pedro Valerga & Ashish Kumar Tewari
Structural Chemistry 2015, 26, 555-563
Flexible dimers 1, 2, and 3 of “pyrazole” derivatives linked with propylene spacer are synthesized and conformational stability in solid, solution, and gaseous states is studied through single crystal X-ray diffraction, 2D NOESY ,and DFT, respectively. The folded conformation of compound 2 is stable in all three states and X-ray diffraction evince that molecule is intramolecularly stacked in reverse face-to-face manner. TEM image of compound 2 exhibits rigid hollow nanospikes with high tendency to form agglomerates.
Face-to-face stacking in sulfonamide based bis-ethylene bridged heteroaromatic dimers
Ranjeet Kumar,‡ Sunil K. Rai,‡ Praveen Singh, Archana Gaurav, Pratima Yadav, Ranjana S. Khanna, Hariom Gupta and Ashish K. Tewari*
RSC Adv., 2015,5, 97205-97211
Four sulfonamide based bis-ethylene bridged heteroaromatic dimers were synthesized for analysis of their structural and conformational properties. Interestingly, all models showed intramolecular offset face-to-face stacking between the tosyl group and heteroaromatic system in their solid state conformations. 1H NMR of the solutions revealed that the conformations were not far off from the solid state stacked geometry. However, gaseous state optimizations of different conformers divulged that the crystal structures were the lowest energy conformers.
Sunil K. Rai, Shaziya Khanam, Ranjana S. Khanna and Ashish K. Tewari*
RSC Adv., 2014,4, 44141-44145
Microwave assisted non-catalytic condensation of 2-cyanoacetamide with aromatic aldehydes, and enolate mediated Michael-type addition to acrylamide followed by oxidative cyclization, produce 2-pyridones in good to excellent yield. Unsymmetrical ketones produce two regioisomeric enolates, therefore thermodynamic and kinetic products of butan-2-one and pentan-2-one have been isolated and fully characterized.
An excellent stable fluorescent probe: Selective and sensitive detection of trace amounts of Hg+2 ions in natural source of water
Ranjana Singh, Sunil K. Rai, Manish K. Tiwari, Anurag Mishra, Ashish K. Tewari, Phool Chand Mishra, Ranjan K. Singh
Chemical Physics Letters 2017, 676, 39-45
The fluorescent and stable aqueous solution of 3-Cyano-4,6-dimethyl-2-pyridone (CDPy) has been used as a probe for selective detection of Hg+2 ions in natural river water. The fluorescence intensity of the probe was reduced on adding Hg+2 ions. The DFT and TD-DFT confirmed that the reduction in fluorescence intensity occurred due to excited state charge transfer between the CDPy molecule and Hg+2 ions. This procedure can be used to detect Hg+2 ions up to a detection limit ∼0.41 μM. It is reproducible with excellent stability (∼10 weeks) and applicable in a wide linear range (3–231 μM).