A-type proanthocyanidin
A type proanthocyanidins are a specific type of proanthocyanidins, which are a class of flavanoid. Proanthocyanidins fall under a wide range of names in the nutritional and scientific vernacular, including oligomeric proanthocyanidins, flavanoids, polyphenols, condensed tannins, and OPCs. Proanthocyanidins were first popularized by French scientist Jacques Masquelier.[1]
Contents
Distribution in plants
A-type linkage is a less common feature in proanthocyanidins with both 4β→8 (B-type) and 2β→O→7 interflavanoid bonds.[2]
A-type proanthocyanidin glycosides can be isolated from cocoa liquor.[3]
Dimers
- Procyanidin A1 is an epicatechin-(2β→7,4β→8)-epicatechin dimer.
- Procyanidin A2 is a dimeric (-)epicatechin.
Other A-type proanthocyanidins can be found in cranberries,[2] in apricots, in cinnamon,[4] in Prunus armeniaca (ent-epiafzelechin-3-O-p-hydroxybenzoate-(4α→8,2α→O→7)-epiafzelechin) and in peanut skins (epicatechin-(2β→O→7, 4β→8)-ent-epicatechin).[5]
Epi-afzelechin-(4β→8, 2β→O→7)-afzelechin (geranin A) and epi-catechin-(4β→8, 2β→O→7)-afzelechin (geranin B) can be found in Geranium niveum.[6]
Trimers
- Selligueain A is a natural sweetener
- Selligueain B can also be isolated from the rhizomes of Selliguea feei.[7]
An A type proanthocyanidins trimer can be found in Lindera aggregata (epicatechin-(4β→8,2β→O→7)-entcatechin-(4β-8)-catechin).[8] This compound shows cytoprotective action against ethanol-induced gastric injury.[9]
In Ecdysanthera utilis (epicatechin-(4β→8,2β→O→7)-epicatechin-(4β→8)-epicatechin and epicatechin-(4β→8)-epicatechin-(4β→8,2β→O→7)-epicatechin-(4β→8)-epicatechin) can be found.[10]
Chemistry
B-type procyanidins (catechin dimers) can be converted to A-type procyanidins by radical oxidation.[11] Fragmentation patterns for A-type proanthocyanidins include heterocyclic ring fission (HRF), retro-Diels-Alder (RDA) fission, benzofuran-forming fission (BFF) and quinone methide fission (QM).[12]
No effect on urinary tract infection
The metabolism of type-A proanthocyanidins is significant since a large number of metabolites are detected in urine and feces soon after ingestion of foods rich in polymers, indicating rapid elimination and absence of physiological effect. Polymeric type-A proanthocyanidins are depolymerized into epicatechin units in the small intestine, then cleaved into smaller phenolic acids with no known biological role.[13]
In vitro, A-type proanthocyanidins isolated from cranberry juice cocktail demonstrated anti-adhesion activity against E. coli binding to urinary tract epithelial cells, whereas B-type proanthocyanidins from grape exhibited minor activity.[14] However, in humans, there is no sufficient clinical evidence that cranberry type-A proanthocyanidins are effective in lowering risk of urinary tract infection.[15][16]
References
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