Flavan-3ol

Flavan-3-ols (sometimes referred to as flavanols) are derivatives of flavans that use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. These compounds include catechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate, proanthocyanidins, theaflavins, thearubigins.

Flavanols (with an "a") are not to be confused with flavonols (with an "o"), a class of flavonoids containing a ketone group.

The single-molecule (monomer) catechin, or isomer epicatechin (see diagram), adds four hydroxyls to flavan-3-ol, making building blocks for concatenated polymers (proanthocyanidins) and higher order polymers (anthocyanidins).

Flavanols possess two chiral carbons, meaning four diastereoisomers occur for each of them.

Catechins are distinguished from the yellow, ketone-containing flavonoids such as quercitin and rutin, which are called flavonols. Early use of the term bioflavonoid was imprecisely applied to include the flavanols, which are distinguished by absence of ketone(s). Catechin monomers, dimers, and trimers (oligomers) are colorless. Higher order polymers, anthocyanidins, exhibit deepening reds and become tannins.

The catechins are abundant in teas derived from the tea plant Camellia sinensis, as well as in some cocoas and chocolates (made from the seeds of Theobroma cacao).

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