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1.
Sridhar Madabhushi Raveendra JillellaKondal Reddy Godala Kishore Kumar Reddy MalluChina Ramanaiah Beeram Narsaiah Chinthala 《Tetrahedron letters》2012,53(39):5275-5279
An efficient and simple method for the synthesis of 2,2-disubstituted-2H-chromenes by one-step cyclocondensation of a phenol with a variety of 1,1-disubstituted propargyl alcohols using BF3·Et2O as the catalyst is described. 相似文献
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A remote 4J(F,H) coupling (F? C(α)? C(O)? N? H) of up to 4.2 Hz in α‐fluoro amides with antiperiplanar arrangement of the C? F and the C?O bonds (dihedral angle F? C? C?O ca. 180°) confirms that previous NMR determinations, using the XPLOR‐NIH procedure, of the secondary structures of β‐peptides containing β3hAla(αF) and β3hAla(αF2) residues were correct. In contrast, molecular‐dynamics (MD) simulations, using the GROMOS program with the 45A3 force field, led to an incorrect conclusion about the relative stability of secondary structures of these β‐peptides. The problems encountered in NMR analyses and computations of the structures of backbone‐F‐substituted peptides are briefly discussed. 相似文献
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Raveendra Panickar Dhanya Ananda Herath Douglas J. Sheffler Nicholas D.P. Cosford 《Tetrahedron》2018,74(25):3165-3170
Benzodiazepinones are privileged scaffolds with activity against multiple therapeutically relevant biological targets. In support of our ongoing studies around allosteric modulators of metabotropic glutamate receptors (mGlus) we required the multigram synthesis of a β-ketoester key intermediate. We report the continuous flow synthesis of tert-butyl 3-(2-cyanopyridin-4-yl)-3-oxopropanoate and its transformation to potent mGlu2/3 negative allosteric modulators (NAMs) in batch mode. 相似文献
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Raveendra I. Mathad Bernhard Jaun Oliver Flögel James Gardiner Markus Löweneck Jeroen D. C. Codée Peter H. Seeberger Dieter Seebach Michael K. Edmonds Florian H. M. Graichen Andrew D. Abell 《Helvetica chimica acta》2007,90(12):2251-2273
To further study the preference of the antiperiplanar (ap) conformation in α‐fluoro‐amide groups, two β‐peptides, 1 and 2 , containing a (2‐F)‐β3hAla and a (2‐F)‐β2hPhe residue, have been synthesized. Their NMR‐solution structures in CD3OH were determined and compared with those of non‐F‐substituted analogs, 3 and 4a . While we have found in a previous investigation (Helv. Chim. Acta 2005 , 88, 266) that a stereospecifically introduced F‐substituent in the central position of a β‐heptapeptide is capable of ‘breaking’ the 314‐helical structure by enforcing the F? C? C?O ap‐conformation, we could now demonstrate that the same procedure leads to a structure with the unfavorable ca. 90° F? C? C?O dihedral angle, enforced by the 314‐helical folding in a β‐tridecapeptide (cf. 1 ; Fig. 4). This is interpreted as a consequence of cooperative folding in the longer β‐peptide. A F‐substituent placed in the turn section of a β‐peptidic hairpin turn was shown to be in an ap‐arrangement with respect to the neighboring C?O bond (cf. 2 ; Fig. 7). Analysis of the non‐F‐substituted β‐tetrapeptides (with helix‐preventing configurations of the two central β2/β3‐amino acid residues) provides unusually tight hairpin structural clusters (cf. 3 and 4a ; Figs. 8 and 9). The skeleton of the β‐tetrapeptide H‐(R)β3hVal‐(R)β2hVal‐(R)β3hAla‐(S)β3hPhe‐OH ( 4a ) is proposed as a novel, very simple backbone structure for mimicking α‐peptidic hairpin turns. 相似文献
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Glättli A Daura X Bindschädler P Jaun B Mahajan YR Mathad RI Rueping M Seebach D van Gunsteren WF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7276-7293
The influence of charged side chains on the folding-unfolding equilibrium of beta-peptides was investigated by means of molecular dynamics simulations. Four different peptides containing only negatively charged side chains, positively charged side chains, both types of charged side chains (with the ability to form stabilizing salt bridges) or no charged side chains were studied under various conditions (different simulation temperatures, starting structures and solvent environment). The NMR solution structure in methanol of one of the peptides (A) has already been published; the synthesis and NMR analysis of another peptide (B) is described here. The other peptides (C and D) studied herein have hitherto not been synthesized. All four peptides A-D are expected to adopt a left-handed 3(14)-helix in solution as well as in the simulations. The resulting ensembles of structures were analyzed in terms of conformational space sampled by the peptides, folding behavior, structural properties such as hydrogen bonding, side chain-side chain and side chain-backbone interactions and in terms of the level of agreement with the NMR data available for two of the peptides. It was found that the presence of charged side chains significantly slows down the folding process in methanol solution due to the stabilization of intermediate conformers with side chain-backbone interactions. In water, where the solvent competes with the solute-solute polar interactions, the folding process to the 3(14)-helix is faster in the simulations. 相似文献
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The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C1) and 6-methoxy-4-azidomethyl coumarin (C2) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ
g
) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ
e
) dipole moments were estimated from Lippert’s, Bakhshievs and Chamma-Viallet’s equations by using the variation of Stoke’s
shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated
by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground
state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating
a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins. 相似文献
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An RP-HPLC method for the simultaneous separation and determination of olanzapine (OLZ) and its process impurities in bulk drugs and pharmaceutical formulations was developed. The separation was accomplished on Inertsil ODS 3V (4.6 mm x 250 mm; particle size 5 microm) column using 0.2 M ammonium acetate (pH = 4.50) and ACN as mobile phase in gradient elution mode. The analytes were monitored by a photo diode array (PDA) detector set at 254 nm and the flow rate was kept at 1.0 mL/min. The chromatographic behavior of all the compounds was examined under variable compositions of different solvents, buffer concentrations, and pH. The method was validated in terms of accuracy, precision, and linearity. Four unknown process impurities observed consistently during the analysis of different batches of OLZ were isolated and characterized by ESI-MS/MS, (1)H NMR, and FT-IR. The proposed RP-HPLC method was successfully applied to the analysis of commercial formulations. The method could be of use not only for rapid and routine evaluation of the quality of OLZ in bulk drug manufacturing units but also for the detection of its impurities in pharmaceutical formulations. 相似文献
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Raveendra M. Melavanki Raviraj A. Kusanur Jagadish S. Kadadevaramath Manohar V. Kulkarni 《Journal of fluorescence》2010,20(6):1175-1180
The fluorescence quenching of 5, 6-benzo-4-azidomethyl coumarin (5BAMC) by aniline have been carried in different solvent
mixtures of benzene (BN) and acetonitrile (AN) at room temperature by steady state fluorescence measurements. The quenching
is found to be appreciable and a positive deviation from linearity was observed in the Stern-Volmer plot for the fluorophore
in all the solvent mixtures. Various parameters for the quenching process have been determined using the extended S-V equation
and have been found to be dependent on the solvent polarity. Further, with the use of finite sink approximation model, it
is concluded that the bimolecular reactions quenching reactions are diffusion limited, and the distance parameter R′ and mutual
diffusion coefficient D are estimated independently. 相似文献