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31.
Conformational Control of Oligo(p‐phenyleneethynylene)s with Intrinsic Substituent Electronic Effects: Origin of the Twist in Pentiptycene‐Containing Systems 下载免费PDF全文
Che‐Jen Lin Dr. Sandip Kumar Kundu Dr. Cheng‐Kai Lin Prof. Jye‐Shane Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14826-14833
Dependence of the backbone planarity of oligo(p‐phenyleneethynylene)s (OPEs) on the intrinsic electronic character of substituents and on the nature of the solvent has been experimentally demonstrated with a series of center‐symmetrical five‐ring systems, pentiptycene‐pentiptycene‐arene‐pentiptycene‐pentiptycene, differing in the substituents on the central arene. In frozen 2‐methyltetrahydrofuran (MTHF), the adjacent pentiptycene units prefer to be in a mutually twisted orientation when the substituents are electron‐withdrawing (F and amido), resulting in a TPPT or TTTT conformation, whereas a planarized PPPP backbone is favored in the case of electron‐donating substituents (alkyl and alkoxy). The propensity to adopt the PPPP form is generally enhanced by replacing MTHF with either methylcyclohexane or mixed ethanol/methanol as solvent. These observations reveal that the twist between adjacent pentiptycene units in OPEs is a consequence of the electronic rather than steric effects of iptycenyl substituents. The electronic effect of iptycenyl substituents is manifested in decreased phenylene π polarizability as the net effect of both electron‐donating hyperconjugation and an electron‐withdrawing inductive effect. Variable‐temperature electronic absorption and emission spectroscopies are the critical tools for this work. Our findings provide important guidelines for conformational and electronic engineering of OPEs and for the design of novel iptycene‐based organic electronic materials. 相似文献
32.
Youngsam Kim Sandip V. Mulay Minsuk Choi Seungyoon B. Yu Sangyong Jon David G. Churchill 《Chemical science》2015,6(10):5435-5439
A phenyl-selenium-substituted coumarin probe was synthesized for the purpose of achieving highly selective and extremely rapid detection of glutathione (GSH) over cysteine (Cys)/homocysteine (Hcy) without background fluorescence. The fluorescence intensity of the probe with GSH shows a ∼100-fold fluorescent enhancement compared with the signal generated for other closely related amino acids, including Cys and Hcy. Importantly, the substitution reaction with the sulfhydryl group of GSH at the 4-position of the probe, which is doubly-activated by two carbonyl groups, occurs extremely fast, showing subsecond maximum fluorescence intensity attainment; equilibrium was reached within 100 ms (UV-vis). The probe selectivity for GSH was confirmed in Hep3B cells by confocal microscopy imaging. 相似文献
33.
Membrane Disruption and Enhanced Inhibition of Cell‐Wall Biosynthesis: A Synergistic Approach to Tackle Vancomycin‐Resistant Bacteria 下载免费PDF全文
Venkateswarlu Yarlagadda Dr. Sandip Samaddar Dr. Krishnamoorthy Paramanandham Dr. Bibek R. Shome Dr. Jayanta Haldar 《Angewandte Chemie (International ed. in English)》2015,54(46):13644-13649
Resistance to glycopeptide antibiotics, the drugs of choice for life‐threatening bacterial infections, is on the rise. In order to counter the threat of glycopeptide‐resistant bacteria, we report development of a new class of semi‐synthetic glycopeptide antibiotics, which not only target the bacterial membrane but also display enhanced inhibition of cell‐wall biosynthesis through increased binding affinity to their target peptides. The combined effect of these two mechanisms resulted in improved in vitro activity of two to three orders of magnitude over vancomycin and no propensity to trigger drug resistance in bacteria. In murine model of kidney infection, the optimized compound was able to bring bacterial burden down by about 6 logs at 12 mg kg?1 with no observed toxicity. The results furnished in this report emphasize the potential of this class of compounds as future antibiotics for drug‐resistant Gram‐positive infections. 相似文献
34.
The synthesis of lairdinol A, a component of the host-selective phytotoxin depsilairdin, was achieved in 12 steps (18% overall yield) without the use of protecting groups starting with the Diels-Alder reaction of (R)-carvone with 3-trimethylsilyloxy-1,3-pentadiene. The key step established the trans ring fusion by preferential epoxidation of a trans-fused enone in an equilibrating mixture of the cis-fused and trans-fused diastereomers (i.e., equivalent to a dynamic kinetic resolution of these isomers). The synthesis confirms the absolute configurations of lairdinol A and its enantiomer, cyperusol C. 相似文献
35.
J.S. Yadav B.V. Subba Reddy Swapan Kumar Biswas Sandip Sengupta P. Vishnumurthy 《Tetrahedron letters》2008,49(6):1034-1036
Phenacyl bromides undergo smooth vic-diallylation and dipropargylation with allyl and propargyl indium reagents generated in situ from metallic indium and allyl or propargyl bromide to produce 4-arylocta-1,7-dien-4-ol derivatives in good yields. Phenacyl chloride and azide also participated effectively in bis-allylation. Similar results are also obtained from in situ generated allyl or propargyl zinc bromide. 相似文献
36.
Realizing spatiotemporal patterns out of a chemical reaction diffusion system remains an experimental challenge owing to the difficulty in overcoming the stringent condition of diffusion driven instability. Herein, by considering the spatially extended Gray-Scott model system, we have investigated how the cross diffusivities of the reactants involved influence the nature and dynamics of spatiotemporal patterns. Our study unravels that in absence of diffusion driven instability, spatially inhomogeneous patterns can be obtained for the Gray-Scott model system, and unstable time dependent patterns can be stabilized just by adjusting cross diffusivities of the reactants. Interestingly, the effect of cross diffusion in presence of the diffusion driven instability can differentially alter the speed of pattern formation, and potentially modify the nature of the spatiotemporal patterns obtained under different parametric conditions. Experimental verification of our findings may allow us to observe spatiotemporal patterns beyond the regime of classical Turing instability. 相似文献
37.
Dr. Uttam Dutta Sandip Porey Sandeep Pimparkar Astam Mandal Jagrit Grover Adithyaraj Koodan Dr. Debabrata Maiti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21017-21022
Biaryl compounds are extremely important structural motifs in natural products, biologically active components and pharmaceuticals. Selective synthesis of biaryls by distinguishing the subtle reactivity difference of distal arene C−H bonds are significantly challenging. Herein, we describe para-selective C−H arylation, which is acheived by a unique combination of a meta-directing group and norbornene as a transient mediator. Upon direct meta-C−H palladation, one-bond relay palladation occurs in presence of norbornene and subsequently para-C−H arylation is achieved for sulfonates, phosphonates and phenols bearing 2,6-disubstitution patterns. The protocol is amenable to electron-deficient aryl iodides. Multisubstituted arenes and phenols are obtained by postsynthetic modification of the products. The protocol allows the synthesis of hexa-substituted benzene by sequential selective distal C−H functionalization. 相似文献
38.
Sandip B. Bharate 《Tetrahedron letters》2006,47(39):7021-7024
The antimalarial robustadials A and B have been synthesized in two steps starting from commercially available phloroglucinol comprising a key biomimetic three-component reaction that involves in situ generation of an o-quinone methide via Knoevenagel condensation and subsequent Diels-Alder cycloaddition with (−)-β-pinene. 相似文献
39.
Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles. 相似文献
40.
Syntheses of Boc-protected 4-amino- and 5-amino-pyrrole-2-carboxylic acid methyl esters have been achieved and the structures of these compounds have been fully characterized by detailed NMR studies. 相似文献