It is a molecule with a 4→8 bond (epicatechin-(4β→8)-catechin).

[2] Proanthocyanidin-B1 can be found in Cinnamomum verum (Ceylon cinnamon, in the rind, bark or cortex), in Uncaria guianensis (cat's claw, in the root), and in Vitis vinifera (common grape vine, in the leaf)[3] or in peach.

[4] Procyanidin B1 can be converted into procyanidin A1 by radical oxidation using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals under neutral conditions.

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