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1.
Microsc Microanal ; 29(2): 437-450, 2023 Apr 05.
Article in English | MEDLINE | ID: mdl-37749737

ABSTRACT

Identifying the operative mode of phase separation [spinodal decomposition (SD) or nucleation-growth (NG)] remains an extremely important area of research. The present work examines this critically in the Fe-Cr system using atom probe tomography (APT) and small angle neutron scattering (SANS), and establishes the framework to distinguish the two different modes of α' phase separation in thermally aged Fe-35 at% Cr and Fe-20 at% Cr alloys. Independent APT analysis determines the mode of phase separation on the basis of (i) the presence/absence of periodic chemical fluctuation through radial distribution function analysis and (ii) interphase interface characteristics (diffuse/sharp). SANS analysis, in contrast, yields virtually indistinguishable correlation peaks for both the modes, which necessitates further investigation of the several different aspects of SANS profiles in the light of APT results. For the first time, key features of SANS profiles have been identified that can unambiguously distinguish SD from NG in the Fe-Cr system: (i) nature of temporal evolution of FWHM of the correlation peak and (ii) appropriate value of γ for fitting with the dynamic scaling model (γ = 6 for SD, Fe-35 at% Cr alloy; γ = 4 for NG, Fe-20 at% Cr alloy).

2.
Chem Commun (Camb) ; 59(75): 11200-11203, 2023 Sep 19.
Article in English | MEDLINE | ID: mdl-37650543

ABSTRACT

A rhodium(III)-catalyzed indole C4-selective cyanation is described using the bench-stable, user-friendly electrophilic cyanation agent N-cyano-N-phenyl-p-toluenesulfonamide (NCTS) as a coupling partner. A suitably positioned weakly coordinating tert-amide group was utilized for this site selectivity. The developed protocol proceeded with a broad scope. [Cp*Rh(MeCN)3][SbF6]2 was found to be an effective Rh(III) catalyst for this transformation. An initial study was carried out to know the photophysical properties of the C4-cyanated indole frameworks.

3.
Chem Sci ; 14(14): 3907-3912, 2023 Apr 05.
Article in English | MEDLINE | ID: mdl-37035703

ABSTRACT

While bromo- and iodocyclizations have recently been successfully implemented, the challenging chlorocyclizations have been scantly investigated. We present a selective and generally applicable concept of chlorination-induced polyene cyclization by utilizing HFIP-chloroiodane networks mimicking terpene cyclases. A manifold of different alkenes was converted with excellent selectivities (up to d.r. >95 : 5). The cyclization platform was even extended to several structurally challenging terpenes and terpenoid carbon frameworks.

4.
Org Lett ; 25(11): 1952-1957, 2023 Mar 24.
Article in English | MEDLINE | ID: mdl-36896989

ABSTRACT

A Pd(II)-catalyzed straightforward oxidative naphthylation of unmasked 2-pyridone derivatives is described using a twofold internal alkyne as a coupling partner. The reaction proceeds through N-H/C-H activation to provide polyarylated N-naphthyl 2-pyridones. An unusual oxidative annulation at the arene C-H bond of the diarylalkyne leads to the formation of polyarylated N-naphthyl 2-pyridones, where the 2-pyridone-attached phenyl ring of the naphthyl ring is polyaryl-substituted. Mechanistic studies and DFT calculations suggest a plausible mechanism based on N-H/C-H activation. The N-naphthyl 2-pyridone derivatives were studied to explore encouraging photophysical properties.

5.
Nat Commun ; 14(1): 813, 2023 Feb 13.
Article in English | MEDLINE | ID: mdl-36781877

ABSTRACT

Terpene cyclases catalyze one of the most powerful transformations with respect to efficiency and selectivity in natural product (bio)synthesis. In such polyene cyclizations, structurally highly complex carbon scaffolds are built by the controlled ring closure of linear polyenes. Thereby, multiple C,C bonds and stereocenters are simultaneously created with high precision. Structural pre-organization of the substrate carbon chain inside the active center of the enzyme is responsible for the product- and stereoselectivity of this cyclization. Here, we show that in-situ formed fluorinated-alcohol-amine supramolecular clusters serve as artificial cyclases by triggering enzyme-like reactivity and selectivity by controlling substrate conformation in solution. Because of the dynamic nature of these supramolecular assemblies, a broad range of terpenes can be produced diastereoselectively. Mechanistic studies reveal a finely balanced interplay of fluorinated solvent, catalyst, and substrate as key to establishing nature's concept of a shape-selective polyene cyclization in organic synthesis.

6.
Org Lett ; 24(8): 1631-1636, 2022 03 04.
Article in English | MEDLINE | ID: mdl-35188395

ABSTRACT

An efficient and straightforward method was developed for the synthesis of heterobiaryls using easily available N-oxides and diazonaphthoquinones under cheap Cu(II) catalysis. The developed method offered QUINOX and related congeners in a simple manner. A wide scope of important heterobiaryls was achieved with high site selectivity. The synthesized naphthols were transformed into the privileged related P,N ligands. Suitable resolution methods can directly afford the corresponding axially chiral heterobiaryls.

7.
Microsc Microanal ; : 1-15, 2021 Dec 02.
Article in English | MEDLINE | ID: mdl-34852863

ABSTRACT

The quantitative characterization of small nano-sized precipitates poses genuine challenges and is often deficient in accuracy due to the inherent limitations inevitably associated with the individual experimental techniques. A convenient solution is to utilize multiple complementary techniques. The present work demonstrates an effective way to reliably quantify nano-sized precipitates using a combination of complementary techniques of atom probe tomography (APT), small angle neutron scattering (SANS), and transmission electron microscopy (TEM). As a case study, the size (radius, r), number density (NP), volume fraction (ϕ), and chemical composition of Cr-rich α' precipitates are determined in Fe­20 at% Cr alloy, thermally aged at 773 K for 1,000 h. This combinatorial approach utilizes the strength of each technique in such a way that the overall accuracy of quantitative precipitation analysis improves significantly. For example, the superior spatial resolution makes TEM the appropriate technique to estimate the size and size distribution of the precipitates, while APT provides the chemical composition. Similarly, SANS analysis incorporates both the size and the compositional information thus derived independently and provides statiscally averaged quantitative analysis overcoming the field-of-view limitations of both TEM and APT. This combinatorial approach improves the accuracy of quantification and provides the true representation of the microstructure.

8.
Chem Rec ; 21(12): 3411-3428, 2021 Dec.
Article in English | MEDLINE | ID: mdl-33913245

ABSTRACT

Nitrogen-containing heterocycles are widely found in various biologically active substrates, pharmaceuticals, natural products and organic materials. Consequently, the continuous effort has been devoted towards the development of straightforward, economical, environmentally acceptable, efficient and ingenious methods for the synthesis of various N-containing heterocycles and their functionalizations. Arguably, one of the most prominent direct strategy is regioselective C-H bond functionalizations which provide the step and atom economical approaches in the presence of suitable coupling partners. In this context, site-selective migratory insertion of metal carbenes/nitrenes to the desired C-H bonds has proven as a useful tool to access various functionalized nitrogen heterocycles. In this personal account, we highlight some of our contemporary development toward constructing N-containing heterocycles and their direct functionalizations via transition metal catalysed C-H bond functionalizations based on migratory insertion of metal-carbenes and nitrenes.


Subject(s)
Nitrogen , Transition Elements , Catalysis , Imines , Methane/analogs & derivatives
9.
Appl Biochem Biotechnol ; 193(7): 2076-2086, 2021 Jul.
Article in English | MEDLINE | ID: mdl-33559759

ABSTRACT

Circular RNAs belong to the class of non-coding RNA molecules, though surprisingly some of them have protein-coding potentials. However, the circular RNA circ-SHPRH is known to code for an unusual protein known as SHPRH-146aa. However, the molecular level details of the protein are not yet identified. It was proposed that the protein has its role in glioblastoma. Therefore, in this work, an attempt was made to decipher the various structural features of SHPRH-146aa. The binding interactions of the protein SHPRH-146aa with its partner protein DTL were also analyzed. The main aim of the work was to decipher the characteristics features of this unusual protein and the region on SHPRH-146aa that would form different types of non-covalent binding interactions both among itself as well as with its binding partner. In this work, we tried to elucidate the various structural and physico-chemical features of the protein as well as its mode of interactions with its binding partner. The study would therefore pave the pathway to design future wet lab experiments to delineate the appropriate structural features of the protein as well as its association with glioblastoma and neuro-degenerative diseases.


Subject(s)
DNA Helicases/chemistry , Peptides/chemistry , Tumor Suppressor Proteins/chemistry , Ubiquitin-Protein Ligases/chemistry , DNA Helicases/genetics , Humans , Peptides/genetics , Protein Structure, Secondary , RNA, Circular/genetics , Tumor Suppressor Proteins/genetics , Ubiquitin-Protein Ligases/genetics
10.
Chem Asian J ; 15(14): 2092-2109, 2020 Jul 16.
Article in English | MEDLINE | ID: mdl-32500612

ABSTRACT

2-Pyridone is a ubiquitous motif in natural products, drug molecules, ligands in catalysis and organic materials. There is a necessity of direct step-economic methods for the construction of 2-pyridone based molecules. Strategically, the primary developments have led to the C3-functionalizations due to the inherent reactivity of this center. Despite this, many elegant transition metal-catalysed methods have been established to introduce versatile functional groups at the C4, C5 and C6-position via direct C-H bond functionalizations. This minireview focuses on the categorized introduction of different functional groups at the 2-pyridone scaffolds beyond C3-selectivity and discusses substrate scope, limitations and plausible mechanistic details.

11.
Chem Commun (Camb) ; 56(9): 1440-1443, 2020 Jan 30.
Article in English | MEDLINE | ID: mdl-31913368

ABSTRACT

An efficient Rh(iii)-catalyzed straightforward strategy was developed for the tandem C4 arylamination/annulation of indole derivatives with anthranil to provide indoloquinoline moieties. This method is simple and regioselective with a wide scope and functional group tolerance. Mechanistic studies revealed the important role of the newly installed azacycle in the conversion of O-protected aldoximes to their cyano derivatives. Studies were carried out to explore the promising photophysical properties of the obtained indoloquinoline derivatives.

12.
Chem Asian J ; 15(3): 360-364, 2020 Feb 03.
Article in English | MEDLINE | ID: mdl-31944607

ABSTRACT

A RhIII -catalyzed strategy was developed for the rapid construction of highly substituted 2-pyridone scaffolds using α,ß-unsaturated oximes and fluorinated diazomalonate. The reaction proceeds through direct, site-selective alkylation based on migratory insertion and subsequent cyclocondensation. A wide substrate scope with different functional groups was explored. The requirement of fluorinated diazomalonate was explored for this transformation. The developed methodology was further extended with the synthesis of the bioactive compound.


Subject(s)
Diazomethane/chemistry , Pyridones/chemistry , Rhodium/chemistry , Catalysis , Halogenation , Kinetics , Pyridones/chemical synthesis
13.
J Phys Condens Matter ; 32(11): 115801, 2020 Mar 13.
Article in English | MEDLINE | ID: mdl-31739303

ABSTRACT

The magnetic state of low temperature martensite phase in Co-substituted Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) has been investigated, in view of numerous conflicting reports of occurrences of spin glass (SG), superparamagnetism (SPM) or long range anti-ferromagnetic (AF) ordering. Combination of DC magnetization, AC susceptibility and small angle neutron scattering (SANS) studies provide clear evidence for AF order in the martensitic phase of Ni45Co5Mn38Sn12 alloy and rule out SPM and SG orders. Identical studies on another alloy of close composition, Ni44Co6Mn40Sn10, point to the presence of SG order in the martensitic phase and the absence of SPM behavior, contrary to earlier reports. SANS results do show the presence of nanometre-sized clusters but they are found to grow in size from 3 nm at 30 K to 11 nm at 300 K, and do not correlate with magnetism in these alloys.

14.
Microsc Microanal ; 25(4): 840-848, 2019 Aug.
Article in English | MEDLINE | ID: mdl-31046856

ABSTRACT

Binary Fe-Cu alloys are effective prototypes for investigating radiation-induced formation and growth of nanometric Cu-rich precipitates (CRPs) in nuclear reactor pressure vessels. In this report, the temporal evolution of CRPs during thermal aging of Fe-Cu binary alloys has been investigated by using complementary techniques such as atom probe tomography (APT) and small-angle neutron scattering (SANS). We report a detailed quantitative evolution of a rarely observed morphological transformation of Cu precipitates from spherical to ellipsoid with a significant change (approximately two times) in aspect ratio, an effect known to be associated with the 9R-3R structural transition of the precipitates. It is demonstrated through APT that the precipitates remain spherical up to 8 h, however, they subsequently convert to oblate ellipsoid upon further aging. SANS analysis also detected signs of this morphological transition in reciprocal space. Furthermore, SANS quantifies evolution of the precipitates and corroborates well with the APT results. Interestingly, the power-law exponent of the temporal evolution for mean size and number density agree reasonably well with the Lifshitz-Slyozov-Wagner model, in spite of the complex morphological evolution of the precipitates.

15.
Chemistry ; 25(12): 3000-3004, 2019 Feb 26.
Article in English | MEDLINE | ID: mdl-30650218

ABSTRACT

An efficient pot-economic and step-economic RhIII -catalyzed site-selective direct amination/annulation strategy was developed for the synthesis of benzophenanthroline derivatives using quinoline N-oxides and anthranils. The method was further extended to the synthesis of nitrogen-containing extended π-conjugated benzophenanthrolinone derivatives. Late-stage functionalizations of cinchonidine and cinchophen derivatives and synthesis of a bioactive quinolino-indole were achieved.

16.
Chem Asian J ; 13(17): 2388-2392, 2018 Sep 04.
Article in English | MEDLINE | ID: mdl-29665279

ABSTRACT

An efficient RhIII -catalyzed redox-neutral method for the direct C8-arylation of quinoline N-oxides using diazonaphthalen-2(1H)-one as coupling partner has been demonstrated. The developed method is simple, scalable and straightforward with a wide range of substrate scope. The applicative potential was extended with a late-stage functionalization and straightforward synthesis of 8-azaBINOL derivative. A plausible reaction pathway was proposed after carrying out preliminary control studies.

17.
J Org Chem ; 82(20): 10989-10996, 2017 10 20.
Article in English | MEDLINE | ID: mdl-28901761

ABSTRACT

A rhodium catalyzed direct regioselective oxidative annulation by double C-H activation is described to synthesize highly substituted quinolones from pyridones. The reaction proceeds at mild conditions with broad scope and wide functional group tolerance. These novel quinolones were explored to recognize nitroaromatic compounds.

18.
J Org Chem ; 82(17): 8933-8942, 2017 09 01.
Article in English | MEDLINE | ID: mdl-28782364

ABSTRACT

An efficient copper(I)-catalyzed direct regioselective arylamination of various heterocyclic N-oxides was achieved successfully under redox-neutral conditions using anthranils as arylaminating reagents. The developed protocol is simple, straightforward, and economic with a broad range substrate scope. The dual functional groups in the final molecules were utilized to construct structurally and functionally diverse nitrogen-containing organic π-conjugated systems.

19.
Chemistry ; 22(39): 13826-13830, 2016 Sep 19.
Article in English | MEDLINE | ID: mdl-27427779

ABSTRACT

An inexpensive copper-catalyzed cascade regioselective alkylation, followed by cyclocondensation of quinoline N-oxides with α-diazo esters has been achieved successfully to provide heteroarene-containing conjugated π-systems. The developed method is simple, straightforward, and economical with a broad range of substrate scope. The dual role of copper catalyst in the C-H bond functionalization and in Lewis acid-promoted cyclization was explored.

20.
J Org Chem ; 81(3): 842-8, 2016 Feb 05.
Article in English | MEDLINE | ID: mdl-26743826

ABSTRACT

A Rh(III)-catalyzed highly efficient C6-alkylation of 2-pyridones has been achieved successfully with α-diazo carbonyl compounds. The developed method is simple, mild, and highly regioselective with a broad range of substrate scope. The regioselectivity is guided by the pyridyl substituent attached to the nitrogen center of the pyridone ring. The directing group can be easily removed, and the only formed byproduct is nitrogen. Furthermore, other similar heterocyclic scaffolds can also be functionalized regioselectively under the developed conditions.

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