B type proanthocyanidin

B type proanthocyanidins are a specific type of proanthocyanidin, which are a class of flavanoids. They are oligomers of flavan-3-ols.

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

Dimeric 4→8 B type proanthocyanidin chemical structure

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

• Procyanidin B1 or epicatechin-(4β→8)-catechin
• Procyanidin B2 or (−)-epicatechin-(4β→8)-(−)-epicatechin
• Procyanidin B3 or catechin-(4α→8)-catechin
• Procyanidin B4 or catechin-(4α→8)-epicatechin

Molecules with 4→6 bonds

chemical structure of a 4-6 dimeric B type proanthocyanidin

• Procyanidin B5 or epicatechin-(4β→6)-epicatechin
• Procyanidin B6 or catechin-(4α→6)-catechin
• Procyanidin B8 or catechin-(4α→6)-epicatechin

Chemistry

B-type procyanidin (catechin dimer) can be converted to A-type procyanidin by radical oxidation.^[1]

Dimeric proanthocyanidins can also be synthesized with procyanidin-rich grape seed extracts reacted with flavan-3-ols under acid catalysis.^[2]

Trimeric B type proanthocyanidins

• Procyanidin C1
• Procyanidin C2

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 by a known procedure.^[3]

Iterative oligomer chemical synthesis

A coupling utilising a C8-boronic acid as a directing group was developed in the synthesis of natural procyanidin B3 (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 C2.^[4]

See also

• Procyanidin dimer