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Proanthocyanidin, Condensed Tannin

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Upper classes : FL Flavonoid


Proanthocyanidin, or condensed (meaning not-hydrolyzable) tannin, is a polymer of flavan-3-ols. Type B is formed from (epi)catechins connected by C4-C6 bond or C4-C8 bond. Type A contains an additional ether bond between C2 and C7. Depending on the unit types, different names may be used.

  • procyanidins ... polymer of (epi)catechins
  • propelargonidins ... polymer of (epi)afzelechins
  • prodelphinidins ... polymer of (epi)gallocatechins

About catechins

Catechins refer to a subgroup of flavan 3-ol derivatives (FL63AC). The two chiral center at C2 and C3 of the flavan 3-ols produces 4 isomers, and (+)-Catechin and its stereoisomer (-)-Epicatechin are naturally abundant. Less abundant are (-)-Catechin and (+)-Epicatechin.

  • afzelechin ... catechin minus 1 hydroxyl group in ring B
  • gallocatechin ... catechin plus 1 hydroxyl group in ring B

Structure FL63ACNS0001.png FL63ACNS0002.png FL63ACNS0004.png FL63ACNS0003.png
Name (+)-Catechin or
(-)-Epicatechin or
ent-Catechin or
ent-Epicatechin or
B-ring stereo
3-Hydroxyl stereo
Afzelechins (+)-Afzelechin (-)-Epiafzelechin ent-Epiafzelechin
Gallocatechins (+)-Gallocatechin (-)-Epigallocatechin ent-Gallocatechin

Among the stereoisomers, the bioavailability in human follows the order:

(-)-epicatechin > (+)-catechin = (+)-epicatechin > (-)-catechin

The circulation level of (-)-epicatechin is 6 times higher than that of (-)-catechin. Naturally abundant species are more bioavailable than less abundant ones.

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