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Molecules 2018, 23(1), 205; https://doi.org/10.3390/molecules23010205

Regioselective Synthesis of Procyanidin B6, A 4-6-Condensed (+)-Catechin Dimer, by Intramolecular Condensation

1
Graduate School of Engineering, Osaka Electro-Communication University (OECU), 18-8 Hatsu-cho, Neyagawa-shi, Osaka 572-8530, Japan
2
College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
3
Department of Pharmaceutical Engineering, Faculty of Engineering, Toyama Prefectural University (TPU), 5180, Kurokawa, Imizu, Toyama 939-0398, Japan
*
Author to whom correspondence should be addressed.
Received: 9 January 2018 / Revised: 15 January 2018 / Accepted: 16 January 2018 / Published: 18 January 2018
(This article belongs to the Special Issue Hit Generation and Verification for Novel Lead Compounds)
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Abstract

Proanthocyanidins, also known as condensed tannins or oligomeric flavonoids, are found in many edible plants and exhibit interesting biological activities. Herein, we report a new, simple method for the stereoselective synthesis of procyanidin B6, a (+)-catechin-(4-6)-(+)-catechin dimer, by Lewis acid-catalyzed intramolecular condensation. The 5-O-t-butyldimethylsilyl (TBDMS) group of 5,7,3′4′-tetra-O-TBDMS-(+)-catechin was regioselectively removed using trifluoroacetic acid, leading to the “regio-controlled” synthesis of procyanidin B6. The 5-hydroxyl group of the 7,3′,4′-tri-O-TBDMS-(+)-catechin nucleophile and the 3-hydroxyl group of 5,7,3′,4′-tetra-O-benzylated-(+)-catechin electrophile were connected with an azelaic acid. The subsequent SnCl4-catalyzed intramolecular condensation proceeded smoothly to give the 4-6-condensed catechin dimer. This is the first report on the complete regioselective synthesis of a 4-6-connected oligomer without modifying the 8-position. View Full-Text
Keywords: condensed tannin; proanthocyanidins; intramolecular condensation; procyanidin B6 condensed tannin; proanthocyanidins; intramolecular condensation; procyanidin B6
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Higashino, Y.; Okamoto, T.; Mori, K.; Kawasaki, T.; Hamada, M.; Nakajima, N.; Saito, A. Regioselective Synthesis of Procyanidin B6, A 4-6-Condensed (+)-Catechin Dimer, by Intramolecular Condensation. Molecules 2018, 23, 205.

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