Leucoanthocyanidins are also referred to as flavan-3,4-cis-diols. They are synthesized from flavanonols via a reduction of the ketone moiety on C4. Examples are leucocyanidin (1.37) and leucodelphinidin (1.38). These compounds are often present in wood and play a role in the formation of condensed tannins.
Because of their completely saturated heterocycle, leucoanthocyanidins, together with flavan-3-ols are referred to as flavans. Examples of flavan-3-ols are catechin (1.39) and gallocatechin (1.40). The 'gallo' in the latter compound refers to the vic-tri-hydroxy substitution pattern on the B-ring. Unlike most other flavonoids, the flavans are present as free aglycones or as polymers of aglycones, i.e. they are not glycosylated.
Catechins (1.41) can also be found as gallic acid esters that are esterified at the 3' hydroxyl group. Note the difference between the gallic acid ester of catechin (1.41) and gallocatechin (1.40).
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