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26 results on '"Dhara, Kalyan"'

2. Live cell single molecule tracking and localization microscopy of bioorthogonally labeled plasma membrane proteins

Author

König, Andres I, Sorkin, Raya, Alon, Ariel, Nachmias, Dikla, Dhara, Kalyan, Brand, Guy, Yifrach, Ofer, Arbely, Eyal, and Roichman, Yael

Abstract

Tracking the localization and mobility of individual proteins in live cells is key for understanding how they mediate their function. Such information can be obtained from single molecule imaging techniques including as Single Particle Tracking (SPT) and Single Molecule Localization Microscopy (SMLM). Genetic code expansion (GCE) combined with bioorthogonal chemistry offers an elegant approach for direct labeling of proteins with fluorescent dyes, holding great potential for improving protein labeling in single molecule applications. Here we calibrated conditions for performing SPT and live-SMLM of bioorthogonally labeled plasma membrane proteins in live mammalian cells. Using SPT, the diffusion of bioorthogonally labeled EGF receptor and the prototypical Shaker voltage-activated potassium channel (Kv) was measured and characterized. Applying live-SMLM to bioorthogonally labeled Shaker Kv channels enabled visualizing the plasma membrane distribution of the channel over time with ∼30 nm accuracy. Finally, by competitive labeling with two Fl-dyes, SPT and live-SMLM were performed in a single cell and both the density and dynamics of the EGF receptor were measured at single molecule resolution in subregions of the cell. We conclude that GCE and bioorthogonal chemistry is a highly suitable, flexible approach for protein labeling in quantitative single molecule applications that outperforms current protein live-cell labeling approaches.

Published
2019

12. Transition-Metal-Free Terminal Alkyne Addition to Isatins.

Author

Dhara, Kalyan, Kapat, Ajoy, Ghosh, Tridev, and Dash, Jyotirmayee

Subjects
*ALKYNES, *ADDITION reactions, *ISATIN, *OXINDOLES, *TRANSITION metal catalysts
Abstract

A ‘direct’ alkynylation of isatins, which uses potassium tert-butoxide to provide the desired 3-hydroxy-3-ethynyl-2-oxindoles in good to high yields, is reported. This protocol proceeds smoothly for both electron-rich and electron-deficient alkynes in comparable reaction rates and does not require any specially design ligand or expensive transition-metal catalysts. [ABSTRACT FROM AUTHOR]

Published
2016
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25. Brønsted Acid-Catalyzed Enantioselective Cycloisomerization of Arylalkynes.

Author

Gicquiaud J, Abadie B, Dhara K, Berlande M, Hermange P, Sotiropoulos JM, and Toullec PY

Abstract

The first example of an enantioselective carbocyclization of an alkyne-containing substrate catalyzed by chiral Brønsted acids was achieved. The use of the 2-hydroxynaphthyl substituent on the alkyne as a directing group constituted the key parameter enabling both efficient regioselective protonation of the carbon-carbon triple bond and chiral induction. The key cationic intermediate could be depicted either as a cationic vinylidene ortho-quinone methide or a stabilized vinyl cation. Atropoisomeric phenanthrenes derivatives were produced in high yields and good enantioselectivities under mild, metal-free reaction conditions in the presence of chiral N-triflylphosphoramide catalysts. The carbenic nature of the cationic intermediate was also exploited to describe an example of alkyne/alkane cycloisomerization., (© 2020 Wiley-VCH GmbH.)

Published
2020
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26. Synthesis of Carbazole Alkaloids by Ring-Closing Metathesis and Ring Rearrangement-Aromatization.

Author

Dhara K, Mandal T, Das J, and Dash J

Subjects
Alkaloids chemical synthesis, Carbazoles chemical synthesis, Cyclization
Abstract

Aprocess for the assembly of carbazole alkaloids has been developed on the basis of ring-closing metathesis (RCM) and ringrearrangement-aromatization (RRA) as the key steps. This method is based on allyl Grignard addition to isatin derivatives to provide smooth access to 2,2-diallyl 3-oxindole derivatives through a 1,2-allyl shift. The diallyl derivatives were used as RCM precursors to afford a novel class of spirocyclopentene-3-oxindole derivatives, which underwent a novel RRA reaction to afford carbazole derivatives. The synthetic sequence to carbazoles was shortened by combining the RCM and RRA steps in an orthogonal tandem catalytic process. The utility of this methodology was further demonstrated by the straightforward synthesis of carbazole alkaloids, including amukonal derivative, girinimbilol, heptaphylline, and bis(2-hydroxy-3-methylcarbazole)., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2015
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