B type proanthocyanidins are a specific type of

proanthocyanidin Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More complex ...

, which are a class of

flavanoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...

s. They are

oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

s of

flavan-3-ol Flavan-3-ols (sometimes referred to as flavanols) are a subgroup of flavonoids. They are derivatives of flavans that possess a 2-phenyl-3,4-dihydro-2''H''-chromen-3-ol skeleton. Flavan-3-ols are structurally diverse and include a range of compo ...

Dimeric B type proanthocyanidins

These molecules have the molecular formula C₃₀H₂₆O₁₂ (molar mass : 578.52 g/mol, exact mass : 578.142426).

Molecules with 4→8 bonds

The 4-8 bond can be in the alpha or in the beta position. *

Procyanidin B1 Procyanidin B1 is a procyanidin dimer. It is a molecule with a 4→8 bond (epicatechin-(4β→8)-catechin). Proanthocyanidin-B1 can be found in ''Cinnamomum verum'' (Ceylon cinnamon, in the rind, bark or cortex), in ''Uncaria guianensis'' (cat's ...

or epicatechin-(4β→8)-catechin *

Procyanidin B2 Procyanidin B2 is a B type proanthocyanidin. Its structure is (−)-Epicatechin-(4β→8)-(−)-epicatechin. Procyanidin B2 can be found in '' Cinchona pubescens'' (Chinchona: in the rind, bark, and cortex), in ''Cinnamomum verum'' (Ceylon cinnam ...

or (−)-epicatechin-(4β→8)-(−)-epicatechin *

Procyanidin B3 Procyanidin B3 is a B type proanthocyanidin. Procyanidin B3 is a catechin dimer (catechin-(4α→8)-catechin). Natural occurrences It can be found in red wine, in barley, in beer, in peach or in '' Jatropha macrantha'', the Huanarpo Macho. H ...

or catechin-(4α→8)-catechin *

Procyanidin B4 Procyanidin B4 is a B type proanthocyanidin. Procyanidin-B4 is a catechin-(4α→8)-epicatechin dimer. It is found in the litchi pericarp, in grape seeds, and, along with 4-cis-isomer of procyanidin B4, in beer.

or catechin-(4α→8)-epicatechin

Molecules with 4→6 bonds

Procyanidin B5 Procyanidin B5 is a B type proanthocyanidin. Procyanidin B5 is an epicatechin-(4β → 6)-epicatechin dimer. Natural occurrences It can be found in grape seeds, in '' Hibiscus cannabinus'' (kenaf) root and bark, and in black chokeberries (''Ar ...

or epicatechin-(4β→6)-epicatechin *

Procyanidin B6 Procyanidin B6 is a B type proanthocyanidin. Procyanidin B6 is a catechin-(4α→6)-catechin dimer. It can be found in grape seeds and in beer.

or catechin-(4α→6)-catechin * Procyanidin B8 or catechin-(4α→6)-epicatechin

Chemistry

B-type procyanidin (

catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...

dimer) can be converted to A-type procyanidin by radical oxidation. Dimeric proanthocyanidins can also be synthesized with procyanidin-rich grape seed extracts reacted with flavan-3-ols under acid catalysis.

Trimeric B type proanthocyanidins

Procyanidin C1 Procyanidin C1 (PCC1) is a B type proanthocyanidin. It is an epicatechin trimer found in grape (''Vitis vinifera''), unripe apples, and cinnamon. Natural occurrence and function Procyanidin C1 can be isolated from grape seed extract. Chemical ...

Procyanidin C2 Procyanidin C2 is a B type proanthocyanidin trimer, a type of condensed tannin. Natural occurrences Procyanidin C2 is found in grape seeds (''Vitis vinifera'') and wine, in barley (''Hordeum vulgare''), malt and beer, in ''Betula spp.'', in ''P ...

Chemical synthesis

A stereoselective synthesis of benzylated catechin trimer under intermolecular condensation is achieved using equimolar amount of dimeric catechin nucleophile and monomeric catechin electrophile catalyzed by AgOTf or AgBF₄. The coupled product can be transformed into

procyanidin C2 Procyanidin C2 is a B type proanthocyanidin trimer, a type of condensed tannin. Natural occurrences Procyanidin C2 is found in grape seeds (''Vitis vinifera'') and wine, in barley (''Hordeum vulgare''), malt and beer, in ''Betula spp.'', in ''P ...

by a known procedure.

Iterative oligomer chemical synthesis

A coupling utilising a C8-

boronic acid A boronic acid is an organic compound related to boric acid () in which one of the three hydroxyl groups () is replaced by an alkyl or aryl group (represented by R in the general formula ). As a compound containing a carbon–boron bond, membe ...

as a directing group was developed in the synthesis of natural

procyanidin B3 Procyanidin B3 is a B type proanthocyanidin. Procyanidin B3 is a catechin dimer (catechin-(4α→8)-catechin). Natural occurrences It can be found in red wine, in barley, in beer, in peach or in '' Jatropha macrantha'', the Huanarpo Macho. H ...

(i.e., 3,4-trans-(+)-catechin-4α→8-(+)-catechin dimer). The key interflavan bond is forged using a novel Lewis acid-promoted coupling of C4-ether 6 with C8-boronic acid 16 to provide the α-linked dimer with high diastereoselectivity. Through the use of a boron protecting group, the new coupling procedure can be extended to the synthesis of a protected procyanidin trimer analogous to natural

.Procyanidin oligomers. A new method for 4→8 interflavan bond formation using C8-boronic acids and iterative oligomer synthesis through a boron-protection strategy. Dennis Eri G., Jeffery David W., Johnston Martin R., Perkins Michael V. and Smith Paul A., Tetrahedron, 2012, volume 68, no 1, pages 340-348,

References

{{procyanidin Condensed tannins