Catechins enantiomer

Both catechin enantiomers are secreted as a racemic mixture through the roots of spotted knapweed (Figure 22.2). (+)-Catechin has antibacterial properties, but (-)-catechin kills other plants with which it comes in contact. In the approximately 100 years since it was accidentally introduced to the United States, spotted knapweed has spread rapidly, replacing native plants over millions of acres and forcing grazing animals to search elsewhere for food. 

Allelopathic processes via (-)-catechia (2S,3R-enantiomer) (Fig. 1) have been invoked to partially explain the snccess of Centaurea maculosa (spotted knapweed) in North America [46-48], Throngh bioassays, root exnded (-)-catechin was identified as the pntative allelochemical of spotted knapweed, and mnltiple stndies have examined varions facets of the role of this compound as an allelochemical [46-51 ]. The 2R,3S-(+)-catechin enantiomer is also produced by the plant, but was reported essentially to be nonphytotoxic. This work supported the novel weapons hypothesis, which states that the success of some exotic invasive plant species may be due to the production of allelochemicals that native species have never encountered and, thus, to which they have not evolved defenses [52]. 

Catechin and epicatechin are two flavanols of the catechin family. They are enantiomers. The capillary zone electrophoresis (CE) methods with UV-detection were developed for quantitative determination of this flavanols in green tea extracts. For this purpose following conditions were varied mnning buffers, pH and concentration of chiral additive (P-cyclodextrin was chosen as a chiral selector). Borate buffers improve selectivity of separation because borate can make complexes with ortho-dihydroxy groups on the flavanoid nucleus. 

The antagonism or prevention of toxic effects may also benefit from stereochemical principles. Thus, optically active flavanones have been shown to inhibit the metabolic activation of the carcinogen benzo[a]pyrene to metabolites that bind covalently to DNA (Chae et al., 1992). Moreover, the (+) enantiomers of 3-0-methyicatechin and catechin have been demonstrated to protect stereoselectively against lipid peroxidation due to paracetamol (Devalia et al., 1982),... 

The protonated species (73/74) presumably also served as precursor to the 4P-deuteriotri-0-methylfisetinidol (82) by delivery of hydride ion from the P-face in a predominant Sn2 mode. Compound (82) persistently formed also when fisetinidol-(4a- 8)- and (4p- 8)-catechin hepta-O-methyl ethers (68) and (70) were treated with Na(CN)BD3 in TEA. This observation prompted an investigation of the structural features of the substrates that direct the stereochemistry of the delivery of hydride ion at C(4) in intermediates of type (73/74). Whereas treatment of the epifisetinidol-(4p- 8)-catechin hepta-O-methyl ether (85) with Na(CN)BD3 afforded the 4P-deuteriotri-0-methylepifisetini-dol (87) (18.5%), tetra-O-methylcatechin (75) (32%) and the (25)-l,3-dideuterio-l,3-diarylpropan-2-ol [6%, enantiomer of compound (80)], the nEfisetinidol-(4p- 8)-catechin hepta-O-methyl ether (86) gave 4a-deuteriotri-O-methyl- nf-fisetinidol [13%, the enantiomer of compound (82)], tetra-O-methylcatechin (75) (24%) and the (25)-l,3-dideuterio-l,3-diarylpropan-2-ol [12%, enantiomer of (80)]. 

Thus, the formation of the 4P-deuteriofisetinidol- and epifisetinidol derivatives (82) and (87) from the reduction of the profisetinidin permethylaryl ethers (68), (70), and (85) with Na(CN)BD3 in TEA, and of the enantiomer of compound (82) during reduction of the fisetinidol-(4p- 8)-catechin derivative (86), indicated that the deuterium ion is consistently delivered to C(4) of a protonated species of type (73 / 74) from the side opposite to the 2-aryl group of the C-ring. This... 

Nay B, Monti JP, Nuhrich A, Deffieux G, Merillon JM, Vercauteren J. Methods in synthesis of flavonoids. Part 2. High yield access to both enantiomers of catechin. Tetrahedron Lett 2000 41 39049-39051. 

Succinoglycan, a sinorhizobial exopolysaccharide, is composed of an octasaccharide subunit. Succinoglycan monomers were isolated and used as chiral shift reagents with NMR spectroscopy for chiral discrimination of catechin. NMR signal splittings were observed in the interactions of saccharides with the enantiomers of catechin. Both chiral separation and discrimination of catechin depend on the presence of succinate substituents of the linear monomeric octasaccharide in capillary electrophoresis and NMR spectroscopy, suggesting that succinylation of sinorhizobial octasaccharide is decisive for the effective chiral separation and discrimination of catechin. 

FIGURE 53.9. Chemical structures of catechin and epicatechin enantiomers. 

FIGURE 53.10. Chromatogram showing the separation of catechin (C) and epicatechin (EC) enantiomers monitored with CD detector at 280 nm and their CD spectra in n-hexane/ethanol (75 25, v/v) doped with 0.1% of TEA (pH 4) on the Chiralcel OD-H column with flow rate of 0.5 mL min. (Reprinted with permission from Reference 49. Copyright [2012] John Wiley Sons, Inc.)... 

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