Polyphenols are a large class of natural products synthesized in plants, for the purposes of plant self-defense and resistance to oxidation by air. Polyphenols belong to the secondary metabolites in natural product chemistry, and contain multi-hydroxy groups (OH) on aromatic rings. Aromatic rings are one or more benzene rings fused together.

Biosynthesis of polyphenols involves sequential condensations of acetylCoA units and other short fatty acetylCoA to form a long linear chain, which is called polyketide chain in natural product chemistry. Enzym-catalyzed folding of a polyketide chain and subsquent enzyme-catalyzed chemical modifications give bio polyphenols of diverse biological activities.

In some case, linear polyketide chains are reduced to saturated or partially saturated linear chains to give long fatty acids via enzyme-catalyzed reactions inside the cells.

Many known antibiotics are polyketide-type natural products as secondary metablites, and may contain multi-aromatic hydroxy groups (OH).

Polyphenols have many sub-classes of compounds, including phenolic acid, stilbene polyphenols, lignans, anthocyanins, flavonols, flavanol including OPC, flavonones, chalcones, etc.. For more details, see: Polyphenols-classification

Catechin and Epicatechin

Catechin and epicatechin are two samll polyphenolic compounds, and the basic building blocks for formation of oligomeric and polymeric proanthocyandins  (OPC and PPC). Green tea is the major source of these two monomers. Red wines are also rich in catechin and epicatechin, mainly from degradation of OPC and PPC during the process of fermentation for wine making. Grape seed extract and pine bark extract contain these 2 monomers in 20-30%. Catechin and epicatechin have been demonstrated a variety of health benefits, but at much lower potency than EGCG and OPC.

Catechin was demonstrated to induce longevity in the nematode worm Caenorhabditis elegans [Mechanisms of Ageing and Development Volume 130, Issue 8, August 2009, Pages 477-486]. Catechin was shown to reduce atherosclerotic lesion development in apo E-deficient mice. (+)- and (−)-catechin may have stereospecific opposite effects on glycogen metabolism in isolated rat hepatocytes. (+)-Catechin exhibits inhibitory effects on intestinal tumor formation in mice. (+)-Catechin slows down and reduces the oxidation of low density lipoprotein. (-)-Catechin suppresses the expression of Kruppel-like factor 7. Catechin was shown to stimulate antifungal effect of amphotericin B against Candida albicans.

The chemical structures of catechin and epicatechin are shown on the left.

Catechin and epicatechin can further form esters from gallic acid and yield catechin or epicatechin gallate can further form esters from gallic acid and yield catechin or epicatechin gallates. These ester derivatives from catechin and epicatechin exists as minor compounds in a variety of plant extract, such as green tea extract, grape seed extract, and pine bark extract.

Epigallocatechin 3-Gallate (EGCG)

EGCG is the most abundant polyphenolic compound in green tea and is a potent antioxidant. Its structure is shown on the left. EGCG has been demonstrated to have a variety of health benefits and therapeutic activities in the treatment of many disorders (e.g. inflamation, cancer, and cardiological problems).

EGCG may decompose or epimerize on heating. As the most significant nutrient in green tea, it partially decomposes or epimerizes upon treatment with hot water. The routine and classical way of tea drink from treatment of green tea with boiling water provide human with somewhat reduced health benefits of EGCG. EGCG is mainly in green teas, but not black teas, as EGCG is converted into thearubigins in black teas. Supplementation of EGCG as green tea extract is necessary to provide sufficient amount of EGCG.

OPC - Oligomeric Proanthocyandin Complex

OPC, -3 initial letter abbreviation of Oligomeric Proanthocyanidin Complex or Oligomeric Procyanidin Complex, is a samll class of polyphenol natural products from plants, and may also be called oligomeric flavanols.

The 3 richest OPC sources are grape seed, pine bark and red wine. Proanthocyanidins include oligomeric proanthocyanidins (OPC) and polymeric proanthocyanidins (PPC). Oligomeric proanthocyanidins can also be referred as to proanthocyanidin oligomers (PCO). Proanthocyanidin and procyanidin are 2 equivalent words without differences in meaning in the commercial market.

The health benefits have been studied in science extensively. See: OPC Health Benefits.

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Catechin chemical structure
Epicatechin chemical structure
EGCG: Epigallocatechin gallate structure
EGCG: Epigallocatechin gallate
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