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

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]

References

^ Conversion of procyanidin B-type (catechin dimer) to A-type: evidence for abstraction of C-2 hydrogen in catechin during radical oxidation. Kazunari Kondo, Masaaki Kurihara, Kiyoshi Fukuhara, Takashi Tanaka, Takashi Suzuki, Naoki Miyata and Masatake Toyoda, Tetrahedron Letters, Volume 41, Issue 4, 22 January 2000, Pages 485-488, doi:10.1016/S0040-4039(99)02097-3
^ New Approach for the Synthesis and Isolation of Dimeric Procyanidins. Nils Köhler, Victor Wray and Peter Winterhalter, J. Agric. Food Chem., 2008, 56 (13), pages 5374–5385, doi:10.1021/jf7036505
^ Efficient Stereoselective Synthesis of Catechin Trimer Derivative Using Silver Lewis Acid-Mediated Equimolar Condensation. Yukiko Oizumi, Yoshihiro Mohri, Yasunao Hattori and Hidefumi Makabe, Heterocycles, 2011, Volume 83, No. 4, pages 739-742, doi:10.3987/COM-11-12159
^ 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, INIST 25254810

[1] Conversion of procyanidin B-type (catechin dimer) to A-type: evidence for abstraction of C-2 hydrogen in catechin during radical oxidation. Kazunari Kondo, Masaaki Kurihara, Kiyoshi Fukuhara, Takashi Tanaka, Takashi Suzuki, Naoki Miyata and Masatake Toyoda, Tetrahedron Letters, Volume 41, Issue 4, 22 January 2000, Pages 485-488, doi:10.1016/S0040-4039(99)02097-3

[2] New Approach for the Synthesis and Isolation of Dimeric Procyanidins. Nils Köhler, Victor Wray and Peter Winterhalter, J. Agric. Food Chem., 2008, 56 (13), pages 5374–5385, doi:10.1021/jf7036505

[3] Efficient Stereoselective Synthesis of Catechin Trimer Derivative Using Silver Lewis Acid-Mediated Equimolar Condensation. Yukiko Oizumi, Yoshihiro Mohri, Yasunao Hattori and Hidefumi Makabe, Heterocycles, 2011, Volume 83, No. 4, pages 739-742, doi:10.3987/COM-11-12159

[4] 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, INIST 25254810

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