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351.
Tushar Kanti Chakraborty Rajib Kumar Goswami Midde Sreekanth 《Tetrahedron letters》2007,48(23):4075-4078
The three chiral centres of the C1-C9 moiety of the six-membered lactone glycosides, lycoperdinosides A and B, have been derived from a common starting material containing a single chiral centre. In contrast, the C10-C21 segment of these molecules has been synthesized using, as key steps, a highly stereoselective aldol reaction, a Ti(III)-mediated opening of a trisubstituted epoxy alcohol and an efficient directed hydrostannylation of a suitably substituted internal alkyne. 相似文献
352.
Sharma AC Jana T Kesavamoorthy R Shi L Virji MA Finegold DN Asher SA 《Journal of the American Chemical Society》2004,126(9):2971-2977
We developed a new sensing motif for the detection and quantification of creatinine, which is an important small molecule marker of renal dysfunction. This novel sensor motif is based on our intelligent polymerized crystalline colloidal array (IPCCA) materials, in which a three-dimensional crystalline colloidal array (CCA) of monodisperse, highly charged polystyrene latex particles are polymerized within lightly cross-linked polyacrylamide hydrogels. These composite hydrogels are photonic crystals in which the embedded CCA diffracts visible light and appears intensely colored. Volume phase transitions of the hydrogel cause changes in the CCA lattice spacings which change the diffracted wavelength of light. We functionalized the hydrogel with two coupled recognition modules, a creatinine deiminase (CD) enzyme and a 2-nitrophenol (2NPh) titrating group. Creatinine within the gel is rapidly hydrolyzed by the CD enzyme in a reaction which releases OH(-). This elevates the steady-state pH within the hydrogel as compared to the exterior solution. In response, the 2NPh is deprotonated. The increased solubility of the phenolate species as compared to that of the neutral phenols causes a hydrogel swelling which red-shifts the IPCCA diffraction. This photonic crystal IPCCA senses physiologically relevant creatinine levels, with a detection limit of 6 microM, at physiological pH and salinity. This sensor also determines physiological levels of creatinine in human blood serum samples. This sensing technology platform is quite general. It may be used to fabricate photonic crystal sensors for any species for which there exists an enzyme which catalyzes it to release H(+) or OH(-). 相似文献
353.
Cyclic homooligomers of a thymidine-based nucleoside amino acid were synthesized from the linear dimer using BOP reagent in the presence of DIPEA under dilute conditions. Conformational analysis by NMR and constrained MD studies revealed that all the cyclic products had symmetrical structures. The NH and CO groups in these molecules point in opposite directions with near perpendicular orientation with respect to the plane of the macrocyclic ring having CO on the same side as the base. 相似文献
354.
N-Phenylacetylphenylhydroxylamine complexes of titanium(IV), yellow in color and extractable into chloroform, with metal:ligand ratios 1:2, 1:3, and 1:4, exist in the acidity ranges of 1–3, 4–7, and 7.5–9.0 N HCl, respectively. The compositions of the complexes were found out by Job's and molar ratio methods. The stepwise and overall formation constants were evaluated following extensions of Yatsimirskii's, Leden's and Harvey and Manning's methods. A computer was used for evaluation of the formation constants of the 1:3 system following the first method. A spectrophotometric method based on solvent extraction technique, for determination of trace amounts of titanium in the presence of diverse ions, has also been described. 相似文献
355.
Tushar Kanti Chakraborty Amit Kumar Chattopadhyay Subhash Ghosh 《Tetrahedron letters》2007,48(7):1139-1142
The formal synthesis of (+)-antimycin A3b and the total synthesis of (+)-blastmycinone were achieved using, as a key step, a method developed by us for the synthesis of 2-methyl-1,3-diols via Ti(III)-mediated diastereo- and regioselective opening of trisubstituted 2,3-epoxy alcohols, to carry out the stereoselective construction of the hydroxy-acid segment. An interesting intramolecular radical translocation took place during the epoxide opening process transforming its vicinal PMB-ether in situ, into an ‘1,2-O-(p-methoxy)benzylidene’ ring. 相似文献
356.
Tushar Kanti Chakraborty Rajarshi Samanta Krishnan Ravikumar 《Tetrahedron letters》2007,48(36):6389-6392
Radical-mediated opening of chiral 2,3-epoxy alcohols, containing suitably positioned β-(alkoxy)acrylate moieties, using Cp2TiCl triggered intramolecular cyclization to give tetrahydrofuran and tetrahydropyran moieties. 相似文献
357.
Tushar Kanti Chakraborty Subhash Ghosh Pasunoori Laxman Shantanu Dutta Rajarshi Samanta 《Tetrahedron letters》2005,46(33):5447-5450
The total synthesis of stevastelin B3 was achieved using, as a key step, a method developed by us for the synthesis of 2-methyl-1,3-diols by Ti(III)-mediated diastereo- and regioselective opening of trisubstituted 2,3-epoxy alcohols, to carry out the stereoselective construction of its propionate-derived fatty acid segment. 相似文献
358.
Tushar K Chakraborty P Srinivasu S Sakunthala Madhavendra S Kiran Kumar Ajit C Kunwar 《Tetrahedron letters》2004,45(18):3573-3577
Conformational analysis of the linear tetramer of the glucose-derived furanoid sugar amino acid 1 by NMR and constrained molecular dynamics studies revealed that the fully protected tetramer 2a has a well-defined structure in CDCl3 with repeating β-turns, each involving a 10-membered ring structure with intramolecular hydrogen bonds between NHi → COi−2. Its deprotected versions 2b and 2c showed aggregation in organic solvents with structures similar to that of 2a. 相似文献
359.
Quinolinic acid forms two complexes with ferrous ion. One is formed at pH 5.9 and has maximum absorption at 420 mμ; the metal to reagent ratio is 1:2 and the instability constant is about 7.10-9. The other complex is formed with an excess of potassium cyanide and shows maximum absorption at 440 mμ; the metal to reagent ratio is 1:1 the instability constant is only 2.73?10-5. The latter complex adheres to Beer's law from 1 to 16 p.p.m. of iron, and its optimum concentration range is 4-16 p.p.m. of iron, where the percent relative error per 1% absolute photometric error is only 2.94.The reagent is highly specific and can be used spectrophotometrically for the determination of very small quantities of iron in presence of many cations. 相似文献
360.
Mukund K. Gurjar Tushar P. KhaladkarRamdas G. Borhade A. Murugan 《Tetrahedron letters》2003,44(28):5183-5187
The Heck reaction between a carbohydrate 5,6-ene derivative 9 and an aromatic halide exclusively gave rise to the β-carbohydrate-substituted trans-styrene derivative 8; while the corresponding Wittig reaction produced a cis/trans mixture in which the cis-isomer predominated. The application of the Heck reaction is described to synthesize the intermediate 5, commonly used in the synthesis of members of the crocacin family. 相似文献