Proanthocyanidin oligomers

On the other hand, the flavan-3-ol units can also be doubly linked by an additional ether bond between C2 07 (A-type). Structural variations occurring in proanthocyanidin oligomers may also occur with the formation of a second interflavanoid bond by C-0 oxidative coupling to form A-type oligomers (Fig. 3) [17,20]. Due to the complexity of this conversion, A-type proanthocyanidins are not as frequently encountered in nature compared to the B-type oligomers. 

Qa dan, F., Petereit, F., and Nahrstedt, A., Prodelphinidin trimers and characterization of a proanthocyanidin oligomer from Cistus albidus, Pharmazie, 58, 416, 2003. 

The various MS methods to determine the molecular composition of the constituent monomeric units in proanthocyanidins oligomers are summarized in Ref. 257. Contributions focusing on proanthocyanidin analysis via the HPLC-MS protocol included a wide range of plant-derived foods and beverages, and are summarized in Refs. 12, 258-261. In addition, references to additional significant contributions in this area are readily available via several of the excellent electronic search engines that are at our disposal. 

Deprez, S., Mila, L, and Scalbert, A., Carbon-14 biolabeling of (+)-catechin and proanthocyanidin oligomers in willow tree cuttings, J. Agric. Food Chem., 47, 4219, 1999. 

H6r, M., Heinrich, M., and Rimpler, H., Proanthocyanidin polymers with antisecretory activity and proanthocyanidin oligomers from Guazuma ulmifolia. Phytochemistry, 42, 109, 1996. 

Lazarus, S.A. et al.. Analysis and purification of proanthocyanidin oligomers. Methods Polyphenol Anal, 267, 2003. 

Figure 8.10 Sequencing the heterogeneous proanthocyanidin oligomers according to quinone methide fragment of inter-flavan bonds.

In their studies on phenols in apples (Ch. 15.4.1), Vrhovsek et al. [59] monitored four anthocyanins. In addition, the proanthocyanidin oligomers were quantified as a group. Catechins and proanthocyanidins account for 71-90% of the phenols in apples. 

Jannie P. J. Marais studied at the University of the Free State, Bloemfontein, South Africa where he obtained his Ph.D. in organic chemistry in 2002. His research focused on characterization of the free phenolic profile of South African red wine, and the stereoselective synthesis of flavonoids, for example, flavan-3,4-diols and flavanones. He joined the National Center for Natural Products Research at the University of Mississippi as a postdoctoral associate in July of 2002, where he worked with Dr. Ferreira on the stereoselective synthesis of flavonoid precursors, the semi-synthesis of proanthocyanidin oligomers, characterization of proanthocyanidin profiles of selected transgenic plants, and the synthesis of radioactive antimalarial 8-aminoquinolines. He was promoted to associate research scientist in 2005, where his main area of research still remains the synthesis of A- and B-type proanthocyanidins, starting at the monomeric level and continuing through the tri- and tetra-meric, to the deca-mer level. 

The elegance of this simple biomimetic approach to the synthesis of proanthocyanidin oligomers was demonstrated during synthesis of the mixed profisetinidin trimers (22) and (23), i.e. analogues possessing different ABC and GHI chain extender units. Triflavanoid (22) with its fisetinidol ABC and epifisetinidol GHI units was formed by acid-catalyzed reaction of fisetinidol-(4a->8)-catechin (24) (57) and epifise-... 

This review clearly demonstrates that considerable progress has been made to gain insight into the complex factors that govern the chemistry of the proanthocyanidin oligomers. It may be anticipated that the rapid advances that have been made in conformational analysis of these compounds will continue and will contribute towards understanding of the intricate principles governing the complexation of proanthocyanidins with other biomolecules. 

The nomencleature for proanthocyanidin oligomers, described in Sect. 7.6.B.3, may be extended to the proanthocyanidin polymers (condensed tannins), which are separated from the oligomers somewhat artificially, for the purposes of this chapter. 

As was first shown by Roux and co-workers, in a detailed study of appropriate model compounds, the sign of the band near 220 nm for the circular dichroism spectra of proanthocyanidin oligomers is determined by the absolute configuration at C-4 and appears to arise largely from interactions between A-ring chromophores (16). Similarly, the sign of an intense couplet near 200 nm is deter-... 

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