@article { ISI:000301128300003, title = {Radical mediated deoxygenation of inositol benzylidene acetals: conformational analysis, DFT calculations, and mechanism}, journal = {Carbohydrate Research}, volume = {351}, year = {2012}, month = {APR}, pages = {26-34}, publisher = {ELSEVIER SCI LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

Xanthates of 1,3-benzylidene acetal derivatives of myo- and neo-inositols undergo dideoxygenation under Barton-McCombie conditions, as a result of intramolecular abstraction of the benzylidene acetal hydrogen and subsequent cleavage of the acetal ring. Scrutiny of structure of these bicyclic inositol derivatives shows that although the conformation of the two rings can vary depending on the configuration of the inositol ring and the phase in which the molecules are present, both the xanthates lead to the formation of the same dideoxyinositol. DFT calculations on these molecular systems suggest that neo-inositol derivatives undergo conformational change prior to radical formation while myo- inositol derivatives undergo conformational change subsequent to radical formation, during the deoxygenation reaction. A low barrier for intramolecular hydrogen transfer supports the extreme facility of this deoxygenation reaction. (C) 2012 Elsevier Ltd. All rights reserved.

}, keywords = {Deoxygenation, DFT, Inositol, Mechanism, Radical, Xanthate}, issn = {0008-6215}, doi = {10.1016/j.carres.2012.01.001}, author = {Gurale, Bharat P. and Vanka, Kumar and Shashidhar, Mysore S.} } @article { ISI:000362308600004, title = {Lannea coromandelica attenuates glucagon and oxyntomodulin mediated cAMP formation in HEK cells stably-expressing human glucagon receptor}, journal = {Journal of Herbal Medicine}, volume = {5}, number = {3}, year = {2015}, month = {SEP}, pages = {153-157}, publisher = {ELSEVIER GMBH, URBAN \& FISCHER VERLAG}, address = {OFFICE JENA, P O BOX 100537, 07705 JENA, GERMANY}, abstract = {

Antagonism of glucagon is a potential therapeutic approach for Type 2 diabetes mellitus (T2DM). The bark extract of Lannea coromandelica has been reported to have hypoglycemic or anti-diabetic effects on animal models and human subjects. The aim of this study was to elucidate the molecular mechanisms of L. coromandelica extract as a glucagon receptor antagonist. The aqueous extract of L. coromandelica bark attenuated glucagon-mediated cAMP formation in a concentration dependent manner with an IC50 value of 4.24 +/- 1.31 mu g/ml. It shifted a concentration response curve of glucagon towards the right with a 4, 21 and 40-fold change in IC50 at 6.25, 12.5 and 25 mu g/ml of extract, respectively. Additionally, it attenuated an oxyntomodulin-mediated cAMP response. The extract was found specifically to inhibit glucagon mediated cAMP formation since it was ineffective in reducing cAMP levels nonspecifically-elevated by forskolin. The data support that the aqueous extract of L. coromandelica antagonizes the glucagon receptor and has the potential to reduce glucagon mediated liver glucose output. (C) 2015 Elsevier GmbH. All rights reserved.

}, keywords = {cAMP, Diabetes, Glucagon, Lannea coromandelica, Mechanism, Oxyntomodulin}, issn = {2210-8033}, doi = {10.1016/j.hermed.2015.06.005}, author = {Walunj, Sameer and Gupta, Rajesh and Joshi, Swati P. and Sabharwal, Sushma G. and Joshi, Kalpana} } @article {45634, title = {Mechanistic and spectroscopic investigations of Ru3+-catalyzed oxidative degradation of azidothymidine by heptavalent manganese at environmentally relevant pH}, journal = {Desalination and Water Treatment}, volume = {57}, year = {2016}, month = {DEC}, pages = {28349-28362}, type = {Article}, abstract = {

The rapid increase in the population across the world has increased the consumption of pharmaceutical substances. These pharmaceutical substances have penetrated into the water through various ways. Mechanistic and spectroscopic investigations of Ru3+-catalyzed oxidative degradation of azidothymidine (AZT) by heptavalent manganese was studied for the first time. The values of pH-dependent apparent second-order rate constant show that Ru3+ accelerates the rate of the oxidative degradation of AZT by heptavalent manganese eight times faster than uncatalyzed reaction. Ru3+ catalytic oxidative degradation of AZT by heptavalent manganese was greatly depending on the pH. The removal of the AZT by heptavalent manganese in the presence of Ru3+ shows unit order with respect to heptavalent manganese, Ru3+, and AZT. The influences of dielectric constant, ionic strength, pH, addition of monomer, variation in catalyst concentration, etc. on the rate of the reaction were studied thoroughly and discussed in detail. The eight different products produced during the reaction were analyzed using the high-resolution mass spectrometry. Activation parameters were determined from variation in temperature during the reaction. The catalytic plausible mechanism was projected in which Ru3+ is oxidized to higher oxidation states of ruthenium by heptavalent manganese at environmentally relevant pH.

}, keywords = {Azidothymidine, catalysis, Degradation, Heptavalent manganese, kinetics, Mechanism}, issn = {1944-3994}, doi = {10.1080/19443994.2016.1187090}, author = {Kulkarni, Raviraj M. and Bhamare, Vijaykumar S. and Santhakumari, B.} } @article {45829, title = {Oxidative transformation of antiretroviral drug zidovudine during water treatment with permanganate: reaction kinetics and pathways}, journal = {Desalination and Water Treatment}, volume = {57}, year = {2016}, month = {FEB}, pages = {24999-25010}, type = {Article}, abstract = {

The presence of the pharmaceutical substances in the water has been reported by many studies and has attracted attention across the world. The mechanistic insight into oxidation of antiretroviral drug zidovudine (ZDV) by potassium permanganate was investigated between the pH values 3.0 and 9.0. The pH-dependent second-order rate constants were determined and rate constants decreased with an increase in pH. The products of the reaction were identified by high-resolution mass spectrometry. A probable mechanism is proposed which involves the formation of an intermediate complex between permanganate and ZDV, which further undergoes degradation in subsequent fast steps to form various oxidized products. The different parameters like effect of initially added products, solvent polarity, ionic strength, temperature, and pH on the rate of the oxidative degradation of ZDV by permanganate were systematically studied. The various activation parameters were determined from the effect of variation in temperature on the oxidative degradation of ZDV by permanganate in acidic medium and discussed in detail.

}, keywords = {Degradation, kinetics, Mechanism, Permanganate, Zidovudine}, issn = {1944-3994}, doi = {10.1080/19443994.2016.1149110}, author = {Kulkarni, Raviraj M. and Bhamare, Vijaykumar S. and Santhakumari, B.} } @article {46356, title = {Medium modulated oxygen reduction activity of Fe/Co active centre-engrafted electrocatalysts}, journal = {ChemElectroChem}, volume = {6}, year = {2019}, month = {JUN }, pages = {2956-2964}, type = {Article}, abstract = {

Iron and cobalt metal atoms are effective active centers for the synthesis of carbon-based noble-metal-free catalysts for the oxygen reduction reaction (ORR) owing to their cost-effective intrinsic activity and tunable properties. Annealing of the active center with the conducting carbon enhances the ORR activity significantly. Herein, we have engrafted Fe and Co active centers in the homemade conducting carbon and the ORR performance has been closely observed under acidic and basic pH conditions to understand the influence of the medium and participating moieties towards the performance. In the half-cell reaction, the onset potential and half-wave potential for ORR are governed by the surface intermediates and concomitantly driven by the adsorption energies of the intermediates over the active centers. The iron and cobalt active center-engrafted carbon catalyst behaves differently in acidic and basic electrolytes owing to the dissociation of the surface intermediates. The iron-based catalyst shows improved onset potential against the cobalt-based one. Similarly, the cobalt-based catalyst shows improved half-wave potential against the iron active-center-grafted catalyst. The combined synergistic effect of the two catalysts is realized in the composition represented as Fe/2Co-N-GVC, where improved onset and half-wave potentials are noted in basic medium. A significant variation in the activity of the catalyst is observed as the medium changes from acidic to basic and the effect is directly associated with the surface adsorption of the intermediates.

}, keywords = {active centers, half-wave potential, Mechanism, oxygen reduction reaction, transition state}, issn = {2196-0216}, doi = {10.1002/celc.201900260}, author = {Kashyap, Varchaswal and Anand, Aljo and Soni, Roby and Sreekumar, Kurungot} } @article {45528, title = {Nickel-catalyzed straightforward and regioselective C-H alkenylation of indoles with alkenyl bromides: scope and mechanistic aspect}, journal = {ACS Catalysis}, volume = {9}, year = {2019}, month = {JAN}, pages = {431-441}, type = {Article}, abstract = {

Nickel-catalyzed regioselective C-H bond alkenylation of indoles and related heteroarenes with alkenyl bromides is accomplished under relatively mild conditions. This method allows the straightforward synthesis of C-2 alkenylated indoles employing an air-stable and well-defined nickel catalyst, (bpy)NiBr2, providing a solution to the limitations associated with hydroindolation and oxidative alkenylation. The reaction conceded the coupling of indole derivatives with various alkenyl bromides, such as aromatic and heteroaromatics, alpha- and beta-substituted as well as exo- and endo-cyclic alkenyl compounds. An extensive mechanistic investigation, including controlled study, reactivity experiments, kinetics and labeling studies, and EPR and XPS analyses, highlights that the alkenylation proceeds through a single-electron transfer process comprising an odd-electron oxidative addition of alkenyl bromide. Furthermore, the alkenylation operates via a probable Ni(I)/Ni(III) pathway involving the rate-limiting C-H nickelation of indole.

}, keywords = {alkenylation, C-H activation, indoles, Mechanism, Nickel, single-electron transfer}, issn = {2155-5435}, doi = {10.1021/acscatal.8b04267}, author = {Jagtap, Rahul A. and Vinod, C. P. and Punji, Benudhar} } @article {47638, title = {Ni(II)-catalyzed intramolecular C-H/C-H oxidative coupling: an efficient route to functionalized cycloindolones and indenoindolones}, journal = {ACS Catalysis}, volume = {11}, year = {2021}, month = {OCT }, pages = {12384-12393}, type = {Article}, abstract = {Nickel(II)-catalyzed intramolecular C(sp(2))-H/C(sp(3))-H and C(sp(2))-H/C(sp(2))-H oxidative couplings in indoles are achieved via chelation assistance. These reactions provide access to biologically relevant five- and six-membered substituted cyclopentaindolones, carbazolones, and indenoindolones in high yields and good chemoselectivity employing an air-stable and defined nickel catalyst, (bpy)Ni(OAc)(2). The oxidative cyclizations proceeded either through a six-membered or an unconventional seven-membered nickelacycle. An extensive mechanistic investigation by experiments and theoretical calculations revealed a facile indole{\textquoteright}s C(2)-H nickelation and a rate-limiting reductive elimination process. This intramolecular oxidative cyclization operates via a probable Ni(II)/Ni(III) pathway involving single-electron oxidation of nickel without the participation of a carbon-based radical.}, keywords = {C-H activation, cycloindolones, indenoindolones, indoles, Mechanism, Nickel, oxidative coupling}, issn = {2155-5435}, doi = {10.1021/acscatal.1c03314}, author = {Ankade, Shidheshwar B. and Samal, Pragnya Paramita and Soni, Vineeta and Gonnade, Rajesh G. and Krishnamurty, Sailaja and Punji, Benudhar} } @article {48083, title = {Efficient route to 3,3 {\textquoteleft}-biindolinylidene-diones by iron-catalyzed dimerization of isatins}, journal = {Chemistry-an Asian Journal}, volume = {17}, year = {2022}, month = {AUG}, pages = {e202200414}, type = {Article}, abstract = {

Iron-catalyzed dimerization of various isatin derivatives is described for the efficient synthesis of 3,3 {\textquoteleft}-biindolinylidene-diones (isoindigos). The reaction provides easy access to self-coupled and cross-coupled 3,3 {\textquoteleft}-indolinylidene-diones that have high relevance to biology and materials. This Fe(0)- or Fe(II)-catalyzed dimerization reaction tolerates a wide range of functionalities, such as fluoro, chloro, bromo, alkenyl, nitrile, ether, ester, pyrrolyl, indolyl and carbazolyl groups, including cyclic and acyclic alkyls as well as an alkyl-bearing fatty-alcohol moiety. Especially, the coupling between two distinct isatins provided excellent selectivity for the cross-dimerization with trace of self-couplings. The single-crystal X-ray diffraction study established the molecular structure of eight dimerized products. A preliminary mechanistic study of the Fe-catalyzed dimerization supported the radical pathway for the reaction.

}, keywords = {Cross-coupling, dimerization, iron, Isatin, Isoindigo, Mechanism}, issn = {1861-4728}, doi = {10.1002/asia.202200414}, author = {Jagtap, Rahul A. and Pradhan, Chandini and Gonnade, Rajesh G. and Punji, Benudhar} } @article {47732, title = {Unraveling the reaction mechanism of selective C9 monomeric phenols formation from lignin using Pd-Al2O3-activated biochar catalyst}, journal = {Bioresource Technology}, volume = {344}, year = {2022}, month = {JAN}, pages = {126204}, type = {Article}, abstract = {The conversion of biomass-derived lignin to valuable monomeric phenols at high selectivity is of paramount importance for sustainable biorefineries. In this study, a novel Pd-Al2O3 supported on activated biochar catalyst is developed for lignin hydrogenolysis. The catalyst characterization revealed that the (1 1 1) planes of both of Pd-0 and Al2O3 were exposed to the surface. The maximum lignin conversion of 70.4\% along with high liquid yield (similar to 57 wt\%) was obtained at 240 degrees C, 3 h and 3 MPa H-2 pressure. The total monomeric phenols yield in the liquid was 51.6 wt\%, out of which C9 monomeric guaiacols constituted similar to 30.0 wt\% with 38.0\% selectivity to 4-propyl guaiacol. Using the reaction intermediate, coniferyl alcohol, chemoselective hydrogenation of C-alpha=C-beta is proved to occur over the Pd site, while dehydroxylation of C-gamma-OH is shown to occur over the alumina site. An impressive carbon atom economy of 60\% was achieved for the production of monomeric phenols.}, keywords = {Hydrogenolysis, lignin, Mechanism, Pd-Al/activated biochar, Propanol guaiacol, Propyl guaiacol}, issn = {0960-8524}, doi = {10.1016/j.biortech.2021.126204}, author = {Gurrala, L. and Kumar, M. M. and Yerrayya, Attada and Kandasamy, Prabu and Castano, Pedro and Raja, T. and Pilloni, Giovanni and Paek, C. and Vinu, R.} }