Doc:FL63AC

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
Name	(+)-Catechin or D-Catechin	(-)-Epicatechin or L-Epicatechin	ent-Catechin or (-)-Catechin	ent-Epicatechin or (+)-Epicatechin
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.