69082-79-7Relevant academic research and scientific papers
Spectroscopic Properties of Free Phenolic 4-Arylflavan-3-ols as Models for Natural Condensed Tannins
Zyl, Pieter W. van,Steynberg, Jan P.,Brandt, Edward V.,Ferreira, Daneel
, p. 1057 - 1063 (2007/10/02)
A unique range of free phenolic 4-arylflavan-3-ols consisting of four sets (3',4',5,7-tertrahydroxyflavan-3-ol or its 5-deoxy analogue coupled to phloroglucinol or resorcinol), each composed of three diastereomers (2,3-trans-3,4-trans, 2,3-trans-3,4-cis and 2,3-cis-3,4-trans) were synthesized to assess their spectroscopic properties. 1H and 13C NMR and circular dichroism data are related to selected structural and stereochemical features with a view to modelling natural phenolic oligoflavanoids. - Key words: 4-Arylflavan-3-ols 1H NMR 13C NMR Circular dichroism Condensed tannins
Synthesis of Condensed Tannins. Part 1. Stereoselective and Stereospecific Syntheses of Optically Pure 4-Arylflavan-3-ols, and Assessment of their Absolute Stereochemistry at C-4 by means of Circular Dichroism
Botha, Jacobus J.,Young, Desmond A.,Ferreira, Daneel,Roux, David G.
, p. 1213 - 1219 (2007/10/02)
Stereoselective and also stereospecific condensation at C-4 of flavan-3,4-diols of known absolute configuration with phloroglucinol and resorcinol in acid medium proceeds at ambient temperatures with partial retention of configuration for 2,3-trans-isomers and with inversion for 2,3-cis-analogues.Circular dichroism spectra of the resultant 4-arylflavan-3-ols all exhibit multiple Cotton effects.The sign of high intensity Cotton effects to low wavelength, contributed by aryl chromophores at C-4, may almost invariably be correlated with the absolute configuration at this chiral centre of 2,3-trans-3,4-trans, 2,3-trans-3,4-cis, and 2,3-cis-3,4-trans-isomers.
Synthesis of Condensed Tannins. Part 2. Synthesis by Photolytic Rearrangement, Stereochemistry, and Circular Dichroism of the First 2,3-cis,3,4-cis-4-Arylflavan-3-ols
Westhuizen, Jan H. van der,Ferreira, Daneel,Roux, David G.
, p. 1220 - 1226 (2007/10/02)
Photolytic rearrangements of those 2,3-trans-3,4-trans- and 2,3-trans-3,4-cis-4-arylflavan-3-ols in which the nucleophilicity of D-ring (4-aryl group) functionality exceeds that of the A-ring, provide the first access to 2,3-cis-3,4-cis-diastereoisomers.The circular dichroism of these new isomers is at variance with the proposed general rule for assessing the absolute configuration at C-4.In terms of the aromatic quadrant rule such discrepancies correlate with deviations from the preferred C-ring conformations.
