Proanthocyanidins, History, Structure, Occurrence and Biological Activity
Proanthocyanidins (PCs) are some of the most abundant polyphenolic substances in the plant kingdom. OPCs are an integral part of the human diet, found in high concentrations in fruits such as apples, pear, tea, hawthorn, grapes, and in chocolate. Due to potent antioxidant activity, PCs have been the subject of recent research, demonstrating anticarcinogenic, anti-inflammatory, antimicrobial, and vasodilatory properties, making them a potentially valuable therapeutic tool for the treatment of a variety of conditions. PCs are present in plants as complex mixtures of polymers with an average degree of polymerization between 4 and 11, usually in association with their composing flavan-3-ols. Structural diversity is possible by variation in hydroxylation pattern, stereochemistry at the three chiral centers, and the location and type of interflavan linkage. The most frequent basic units of proanthocyanidins are derivatives of flavan-3-ols: (+)-catechin, (-)-epicatechin, (+)-gallocatechin, (-)-epigallocatechin (EGC) and (-)-epigallocatehin gallate (EGCG).
PCs, naturally occurring antioxidants widely available in fruits, vegetables, nuts, seeds, flowers and bark, have been reported to possess a broad spectrum of biological, pharmacological and therapeutic activities against free radicals and oxidative stress. Epicatechin, dimeric procyanidin B2 and B5, proanthocyanidin A2 and trimeric procyanidin C1 of Crataegus sinaica Boiss. and/or Adansonia digitata L. display potent antioxidant antiviral properties in vitro.
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