Discrimination of α-Amino Acids Using Green Tea Flavonoid (−)-Epigallocatechin Gallate as a Chiral Solvating Agent

Abstract

We report a special, hitherto-unexplored property of (-)-epigallocatechin gallate (EGCG) as a chiral solvating agent for enantiodiscrimination of α-amino acids in the polar solvent DMSO. This phenomenon has been investigated by (1)H NMR spectroscopy. The mechanism of the interaction property of EGCG with α-amino acids has been understood as arising out of hydrogen-bonded noncovalent interactions, where the -OH groups of two phenyl rings of EGCG play dominant roles. The conversion of the enantiomeric mixture into diastereomers yielded well-resolved peaks for D and L amino acids permitting the precise measurement of enantiomeric composition. Often one encounters complex situations when the spectra are severely overlapped or partially resolved hampering the testing of enantiopurity and the precise measurement of enantiomeric excess (ee). Though higher concentration of EGCG yielded better discrimination, the use of lower concentration being economical, we have exploited an appropriate 2D NMR experiment in overcoming such problems. Thus, in the present study we have successfully demonstrated the utility of the bioflavonoid (-)-EGCG, a natural product as a chiral solvating agent for the discrimination of large number of α-amino acids in a polar solvent DMSO. Another significant advantage of this new chiral sensing agent is that it is a natural product and does not require tedious multistep synthesis unlike many other chiral auxiliaries.

Micropatterning of TCR and LFA-1 ligands reveals complementary effects on cytoskeleton mechanics in T cells

“…This indicated that addition of LFA-1 signalling to the system was enhancing the cytoskeletal tension. This is in agreement with the idea of a contractile cytoskeleton across the IS (which is suggested by centripetal motion of microclusters for cells on lipid bilayers 27, 28 ) and was also confirmed by blebbistatin treatment, which reduced the free-edge radii on the OKT3/ICAM-1 but not the OKT3/OKT3 grids. Intriguingly, cell spreading along ICAM-1 decreased with blebbistatin treatment, suggesting that LFA-1 function, like that of other integrins, is reinforced by cell contractility.…”

“…Both Arp2/3 and HS1 (a stabilizer of Arp2/3 branching 28, 31 , Fig. 3A) localized preferentially to the OKT3 lines, consistent with a role of TCR signalling in promoting cell anchorage and extension on these surfaces.…”

Synthesis of Peptides Containing C-Terminal Esters Using Trityl Side-Chain Anchoring: Applications to the Synthesis of C-Terminal Ester Analogs of the Saccharomyces cerevisiae Mating Pheromone a-Factor

“…Both peptides exhibited essentially identical retention times, suggesting that it would not be possible to employ chromatographic methods to investigate possible Cys epimerization in the context of this larger peptide. Since NMR spectroscopy has also been used to analyze the stereochemical composition of mixtures of diastereomeric peptides 28 and complexes of D , L -amino acids, 29 that technique was employed here. Inspection of the fingerprint region of a 2D 1 H- 1 H TOCSY NMR spectrum obtained using 8a (Figure 2A) shows a single doublet due to Hα-HN coupling.…”

RNA nucleosides as chiral sensing agents in NMR spectroscopy

“…14,15 The easy accessibility and available experimental techniques make NMR an important analytical tool for chiral analysis. [22][23][24][25][26][27][28][29][30][31][32] Recently, several studies have been reported on bio-molecular chiral sensing, which used DNA, xanthan, folic acid and guanosine based weak chiral aligning media to differentiate enantiomers using NMR. Number of chiral auxiliaries have been reported for efficient differentiation of enantiomers, assignment of the absolute configuration and also for the measurement of the enantiomeric excess (ee).…”

“…NMR differentiates enantiomers through chiral auxiliaries [7][8][9][10][16][17][18] and through chiral alignment media, [19][20][21] which induce diastereomeric interactions and a differential ordering effect (DOE) respectively. 19,20,33,34 There are also reports of DNA and polysaccharide based chiral stationary phases in chromatography to differentiate enantiomeric peptides and other chiral molecules, 27,35,36 epigallocatechin gallate (EGCG) as a chiral solvating agent to differentiate chiral amino acids 24 and nucleotides for recognition of L-cysteine and D-cysteine by the colorimetric technique. [7][8][9][10][16][17][18] Most of these auxiliaries are synthetically designed that requires more time, synthetic skills and is also uneconomical.…”