Browsing by Author "Anoop S. Singh"

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1-(Hydroxymethyl)-1H-benzotriazole: An Efficient Ligand for Copper-Catalyzed Ullmann-Type Coupling Reaction Leading to Expeditious Synthesis of Diverse Benzoxazoles and Benzothiazoles
(Wiley-Blackwell, 2019) Mala Singh; Priyanka Bose; Anoop S. Singh; Vinod K. Tiwari
Cu-catalyzed Ullmann coupling was performed for the facile synthesis of diverse benzoxazoles and benzothiazoles in the presence of 1-(hydroxymethyl)-1H-benzotriazole as ligand and K2CO3 as base in anhydrous DMF at 120 0C. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
A dinuclear copper(i) thiodiacetate complex as an efficient and reusable 'click' catalyst for the synthesis of glycoconjugates
(Royal Society of Chemistry, 2017) Neha Sareen; Anoop S. Singh; Vinod K. Tiwari; Rajni Kant; Subrato Bhattacharya
We report herein the facile synthesis and structural characterization of a highly stable dinuclear Cu(i) complex, [(PPh3)2Cu(μ-tda)Cu(PPh3)2]·6H2O 1 (tda = thiodiacetate anion), in which the Cu-Cu distance is 7.197 Å. This "pre-formed" complex serves as an extremely efficient and recyclable homogeneous catalyst (2 mol%, 30 min) for CuAAC in dichloromethane solvent. The synthesis of a variety of glycoconjugates under ambient conditions is successfully achieved using 1 as a catalyst. The products are obtained in high yields and very short reaction times while complying with the "click protocols". A simpler procedure solely involving the mixing of substrates with 1 (i.e. base free and solvent free) gave the corresponding glycoconjugate in 10 min using 2 mol% of the catalyst. © The Royal Society of Chemistry 2017.
A new methodology for the synthesis of N-acylbenzotriazoles
(Arkat, 2017) Anoop S. Singh; Anand K. Agrahari; Mala Singh; Nidhi Mishra; Vinod K. Tiwari
A facile and economic path for an easy access of diverse N-acylbenzotriazoles from carboxylic acid has been devised using NBS/PPh3 in anhydrous dichloromethane. High yield of product was obtained at room temperature in one hour reaction time under mild reaction conditions. ©ARKAT USA, Inc
A new methodology for the synthesis of N-acylbenzotriazoles
(Arkat, 2017) Anoop S. Singh; Anand K. Agrahari; Mala Singh; Nidhi Mishra; Vinod K. Tiwari
A facile and economic path for an easy access of diverse N-acylbenzotriazoles from carboxylic acid has been devised using NBS/PPh3 in anhydrous dichloromethane. High yield of product was obtained at room temperature in one hour reaction time under mild reaction conditions. © ARKAT USA, Inc
An efficient one-pot synthesis of: N, N ′-disubstituted ureas and carbamates from N -acylbenzotriazoles
(Royal Society of Chemistry, 2016) Anoop S. Singh; Dhananjay Kumar; Nidhi Mishra; Vinod K. Tiwari
A facile and high-yielding one-pot synthesis of carbamates and N,N′-disubstituted symmetrical ureas from N-acylbenzotriazoles has been devised. It is believed that, the intermediate acyl-azide undergo Curtius rearrangement and in different solvents gives different products i.e. carbamates in alcohols and N,N′-disubstituted symmetrical urea in THF. © The Royal Society of Chemistry 2016.
An Improved N-Acylation of 1 H-Benzotriazole Using 2,2′-DipyridylÂ-diÂ-sulfide and Triphenylphosphine
(Georg Thieme Verlag, 2019) Anoop S. Singh; Anand K. Agrahari; Nidhi Mishra; Mala Singh; Vinod K. Tiwari
A novel path has been developed for the conversion of carboxylic acids into the corresponding N-acylbenzotriazoles by using 2,2′-dipyridyl disulfide/PPh 3 in anhydrous dichloromethane in the presence of 1 H-benzotriazole. Mild reaction conditions, short reaction time, easy in handling, wide substrate scope, availability of reagents involved, and moreover avoiding the use of base makes this protocol quite useful for the laboratory practices for N-acylbenzotriazole synthesis. © Georg Thieme Verlag Stuttgar.
An Improved Synthesis of Urea Derivatives from N -Acylbenzotriazole via Curtius Rearrangement
(Georg Thieme Verlag, 2019) Anoop S. Singh; Anand K. Agrahari; Sumit K. Singh; Mangal S. Yadav; Vinod K. Tiwari
The good leaving tendency of the benzotriazole moiety has been exploited for the synthesis of symmetric, unsymmetric, N -acyl, and cyclic ureas in good yields from N -acylbenzotriazoles by treating the latter with various amines in the presence of TMSN 3 /Et 3 N in a sealed tube. The salient features of the devised protocol includes the high-yield, mild, metal-free, one-pot reaction conditions, and short reaction time. Furthermore, in many cases, no column chromatography is required for the purification. © Georg Thieme Verlag Stuttgart New York.
An Improved Synthetic Protocol for Benzothiazoles via Ring Opening of Benzotriazole
(Wiley-Blackwell, 2018) Dhananjay Kumar; Anoop S. Singh; Vinod K. Tiwari
An improved procedure for the construction of benzothiazole scaffold via intramolecular cyclative cleavage of benzotriazole ring under free radical condition was successfully accomplished. The protocol utilises NaBH4 which regenerates the active reagent n-Bu3SnH in the reaction medium and makes this method cost effective and less toxic as a substitute of expensive and toxic silanes. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
An unexpected p-Toluenesulfonic acid catalyzed 1,3-migration of thiocarbonyl: Selective formation of 1,3-dioxolane-2-thione ring and optimization study
(Association of Carbohydrate Chemists and Technologists, 2014) Dhananjay Kumar; Anoop S. Singh; Vinod K. Tiwari
The selective opening of 5, 6-O-acetal of 3-O-(1,2: 5,6-di -O-i sopropylidine-α-D-gl ucofuranose)-1H-benzo [d][1,2,3]triazole-1-carbothioate (3) afforded bis(1,2-O-isopropylidene-5,6-thionocarbonato-α-D-glucofuranose (5) as a sole crystalline product. The reaction involved the treatment of 3 with p-toluenesulfonic acid in CH2 Cl2 at ambient temperature for 12 h giving compound 5 in 96% yield via 1,3-migration of thiocarbonyl moiety. The optimization study further revealed that the five membered dioxolane-2-thione ring was stabilized over six member ring by 8.78 kcal/mol.
An unprecedented deoxygenation protocol of benzylic alcohols using bis(1-benzotriazolyl)methanethione
(Royal Society of Chemistry, 2015) Dhananjay Kumar; Anoop S. Singh; Vinod K. Tiwari
A facile and regioselective two-step protocol for the deoxygenation of benzylic alcohols using bis(benzotriazole)methanethione has been devised. Benzotriazole derivatives, namely, benzyloxythioacylbenzotriazoles (ROCSBt), on reaction with silanes or Bu3SnH under microwave irradiation or conventional heating undergo a free radical β-scission of C-O bond instead of N-N bond (benzotriazole ring cleavage) to afford a deoxy product. The methodology has various applications because it selectively deoxygenates benzylic alcohols with the aid of a relatively nontoxic (TMS)3SiH reagent as an acceptable alternate to Bu3SnH. © The Royal Society of Chemistry 2015.
An Unprecedented Synthesis of N-Phenyl Amides via Cleavage of Benzotriazole Ring under Free Radical Condition
(Wiley-Blackwell, 2017) Anoop S. Singh; Dhananjay Kumar; Nidhi Mishra; Vinod K. Tiwari
An attempt of Bu3SnH mediated cyclization of acylbenzotriazoles (RCOBt) to corresponding benzoxazole failed; instead, corresponding N-phenylamides were achieved in good yield. The reactions proceed via reductive cleavage of benzotriazole ring with consequent evolution of molecular nitrogen (N2). A diverse range of amide has been achieved in high yields. Structures of all the compounds have been elucidated using IR, MS, 1H and 13C NMR, while four of them (3 o, 3 w, 4 and 5) have also been characterized by single crystal X-ray analysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Benzotriazole as an Efficient Ligand in Cu-Catalyzed Glaser Reaction
(American Chemical Society, 2019) Mala Singh; Anoop S. Singh; Nidhi Mishra; Anand K. Agrahari; Vinod K. Tiwari
Benzotriazole has been established as an efficient ligand in Cu-catalyzed cross-coupling of terminal alkynes to form 1,3-dialkynes using CuI as the catalyst and K2CO3 as the base at room temperature in an open round-bottom flask. The established protocol has the following notable advantages: simple to handle, easy work-up, mild reaction condition, high substrate scope, requirement of less quantity of ligand and also Cu-catalyst, less expensive, and high reaction yield. © 2019 American Chemical Society.
Benzotriazole ring cleavage methodology under free radical condition: an ample opportunity in organic synthesis
(Elsevier, 2024) Mangal S. Yadav; Abhishek Gupta; Anoop S. Singh; Vinod K. Tiwari
Since long back, benzotriazoles have been used as valuable synthons in organic synthesis. Because of their distinctive structural domain, this favors denitrogenation for easy access to biologically relevant molecules through the benzotriazole ring cleavage (BtRC) methodology followed by the generation of new bonds. Recent developments in transition metal–catalyzed coupling reactions have produced a variety of functionalizations of benzotriazoles as constituents of ortho-amino arene diazonium, primarily including cyclization, arylation, alkenylation, alkylation, carbonylation, and the formation of carbon-heteroatom bonds. In this chapter, we briefly emphasize the growing impact of BtRC methodology exploited under free-radical conditions with their notable features and applications in organic synthesis. © 2024 Elsevier Inc. All rights are reserved including those for text and data mining AI training and similar technologies.
Catalytic activity of new heteroleptic [Cu(PPh3)2(β-oxodithioester)] complexes: Click derived triazolyl glycoconjugates
(Royal Society of Chemistry, 2019) Kavita Kumari; Anoop S. Singh; Krishna K. Manar; Chote Lal Yadav; Vinod K. Tiwari; Michael G.B. Drew; Nanhai Singh
A series of four new and two known luminescent heteroleptic Cu(i) complexes of the form [Cu(PPh3)2(β-oxodithioester)] (β-oxodithioester = methyl-3-hydroxy-3-(2-furyl)-2-propenedithioate L1 1, methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate L2 2, methyl-3-hydroxy-3-(4-methoxyphenyl)-2-propenedithioate L3 3, methyl-3-hydroxy-3-(4-bromophenyl)-2-propenedithioate L4 4, methyl-3-hydroxy-3-benzyl-2-propenedithioate L5 5 and methyl-3-hydroxy-3-(3-pyridyl)-2-propenedithioate, L6 6) have been synthesized and characterized by elemental (C, H, N) analysis, and IR, UV-visible, 1H, 13C{1H}, and 31P{1H} NMR spectroscopy and their structures have been ascertained by X-ray crystallography. These complexes were exploited as catalysts for azide-alkyne cycloaddition reactions (click chemistry) for the synthesis of triazolyl glycoconjugates, where they displayed efficient catalytic activity at room temperature. Optimization of the reaction conditions and formation of regioselective products in high yields in the absence of a base/additive are concomitant with the click protocol. The substrate scope was successfully extended by varying the types of sugar azides and alkyne scaffolds, affording the corresponding triazole products in excellent yields at low catalyst loadings (1 mol%). Furthermore, catalyst 1 showed excellent recyclability and was reused for five cycles with little decrease in efficiency. © 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Click inspired synthesis of hexa and octadecavalent peripheral galactosylated glycodendrimers and their possible therapeutic applications
(Royal Society of Chemistry, 2019) Anand K. Agrahari; Anoop S. Singh; Ashish Kumar Singh; Nidhi Mishra; Mala Singh; Pradyot Prakash; Vinod K. Tiwari
A Cu(i)-catalyzed azide-alkyne 1,3-dipolar cycloaddition reaction (CuAAC) has been utilized for the synthesis of novel glycodendrimers containing a rigid hexapropargyloxy benzene centered core with 6- and 18-peripheral β-d-galactopyranosidic units. Structures of the novel glycodendrimers and intermediates were well elucidated using nuclear magnetic resonance and infrared spectroscopies, matrix assisted laser desorption/ionization mass spectrometry, and size-exclusion chromatography. The therapeutic evaluations of the developed glycodendrimers were investigated and they were found to have good potential as anti-bacterial, anti-biofilm, and anti-tumour agents. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019.
Click Inspired Synthesis of Novel Cinchonidine Glycoconjugates as Promising Plasmepsin Inhibitors
(Nature Research, 2020) Nidhi Mishra; Anand K. Agrahari; Priyanka Bose; Sumit K. Singh; Anoop S. Singh; Vinod K. Tiwari
Among all the malaria parasites, P. falciparum is the most predominant species which has developed drug resistance against most of the commercial anti-malarial drugs. Thus, finding a new molecule for the inhibition of enzymes of P. falciparum is the pharmacological challenge in present era. Herein, ten novel molecules have been designed with an amalgamation of cinchonidine, carbohydrate moiety and triazole ring by utilizing copper-catalyzed click reaction of cinchonidine-derived azide and clickable glycosyl alkynes. The molecular docking of developed molecules showed promising results for plasmepsin inhibition in the form of effective binding with target proteins. © 2020, The Author(s).
Click inspired synthesis of: P-tert -butyl calix[4]arene tethered benzotriazolyl dendrimers and their evaluation as anti-bacterial and anti-biofilm agents
(Royal Society of Chemistry, 2020) Anand K. Agrahari; Ashish K. Singh; Anoop S. Singh; Mala Singh; Pathik Maji; Shivangi Yadav; Sanchayita Rajkhowa; Pradyot Prakash; Vinod K. Tiwari
Calixarenes with their three-dimensional structural architecture and ease of functionalization at the upper and/or lower rim are well-known for their plethora of applications in chemical, physical, biological and other disciplines. Herein, CuAAC click inspired p-tert-butylcalix[4]arene tethered benzotriazolyl dendrimers, for example, N-1, N-2 type 2-fold compound 6 and 7 'G(0)' and 6-fold compound 16 and 17 'G(1)' generation benzotriazolyl dendrimer, were devised and also evaluated for their therapeutic potential both in vitro and in vivo. The developed calix[4]arene tethered benzotriazolyl dendrimers have been characterized by standard spectroscopic analysis including NMR (1H and 13C), MS, and SEC. Among all the benzotriazolyl dendrimers developed, compound 7 was identified as the effective one which provided potential anti-bacterial and anti-biofilm activities against drug-resistant and slime producing organisms without imparting cytotoxicity to the eukaryotic systems. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications
(American Chemical Society, 2021) Anand K. Agrahari; Priyanka Bose; Manoj K. Jaiswal; Sanchayita Rajkhowa; Anoop S. Singh; Srinivas Hotha; Nidhi Mishra; Vinod K. Tiwari
Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology. ©
Cu-Catalyzed Click Reaction in Carbohydrate Chemistry
(American Chemical Society, 2016) Vinod K. Tiwari; Bhuwan B. Mishra; Kunj B. Mishra; Nidhi Mishra; Anoop S. Singh; Xi Chen
Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences. © 2016 American Chemical Society.
d-Glucosamine as the Green Ligand for Cu(I)-Catalyzed Regio- And Stereoselective Domino Synthesis of (Z)-3-Methyleneisoindoline-1-ones and (E)- N-Aryl-4 H-thiochromen-4-imines
(American Chemical Society, 2021) Sumit K. Singh; Mangal S. Yadav; Anoop S. Singh; Anand K. Agrahari; Nidhi Mishra; Sunil Kumar; Vinod K. Tiwari
d-Glucosamine, a natural, inexpensive, and conveniently accessible sugar, has been explored as an efficient ligand for the Cu(I)-catalyzed regio- and stereoselective synthesis of an array of (Z)-3-methyleneisoindoline-1-ones and (E)-N-aryl-4H-thiochromen-4-imines in good-to-excellent yield in a tandem fashion via the reaction of 2-halobenzamide and 2-halobenzothioamide with terminal alkynes, respectively. The water solubility and biocompatible nature of the ligand offer easy separation of the catalytic system toward the aqueous phase as well as change in the reaction path in terms of the product also demonstrated the variation of the reaction temperature. The domino reaction proceeds by the Sonogashira and Ullmann type cross-coupling reaction, followed by Cu(I)-promoted additive cyclization of heteroatom to the triple bond. In addition, d-glucosamine causes successful Glaser-Hay coupling of terminal alkynes under Cu catalysis to produce a high yield of respective 1,3-diynes. © 2021 The Authors. Published by American Chemical Society.