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Structure–Activity Relationship of Oligomeric Flavan-3-ols: Importance of the Upper-Unit B-ring Hydroxyl Groups in the Dimeric Structure for Strong Activities

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Graduate School of Engineering, Osaka Electro-Communication University (OECU), 18-8 Hatsu-cho, Neyagawa-shi, Osaka 572-8530, Japan
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Faculty of Engineering, Osaka Electro-Communication University (OECU), 18-8 Hatsu-cho, Neyagawa-shi, Osaka 572-8530, Japan
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Department of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
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Biotechnology Research Center and Department of Biotechnology, Toyama Prefectural University, 5180, Kurokawa, Imizu, Toyama 939-0398, Japan
*
Authors to whom correspondence should be addressed.
Academic Editor: Thomas J. Schmidt
Molecules 2015, 20(10), 18870-18885; https://doi.org/10.3390/molecules201018870
Received: 30 June 2015 / Revised: 3 October 2015 / Accepted: 7 October 2015 / Published: 16 October 2015
(This article belongs to the Section Natural Products Chemistry)
Proanthocyanidins, which are composed of oligomeric flavan-3-ol units, are contained in various foodstuffs (e.g., fruits, vegetables, and drinks) and are strongly biologically active compounds. We investigated which element of the proanthocyanidin structure is primarily responsible for this functionality. In this study, we elucidate the importance of the upper-unit of 4–8 condensed dimeric flavan-3-ols for antimicrobial activity against Saccharomyces cerevisiae (S. cerevisiae) and cervical epithelioid carcinoma cell line HeLa S3 proliferation inhibitory activity. To clarify the important constituent unit of proanthocyanidin, we synthesized four dimeric compounds, (−)-epigallocatechin-[4,8]-(+)-catechin, (−)-epigallocatechin-[4,8]-(−)-epigallocatechin, (−)-epigallocatechin-[4,8]-(−)-epigallocatechin-3-O-gallate, and (+)-catechin-[4,8]-(−)-epigallocatechin and performed structure–activity relationship (SAR) studies. In addition to antimicrobial activity against S. cerevisiae and proliferation inhibitory activity on HeLa S3 cells, the correlation of 2,2-diphenyl-l-picrylhydrazyl radical scavenging activity with the number of phenolic hydroxyl groups was low. On the basis of the results of our SAR studies, we concluded that B-ring hydroxyl groups of the upper-unit of the dimer are crucially important for strong and effective activity. View Full-Text
Keywords: condensed tannins; oligomeric flavonoid; synthesis; DPPH radical scavenging activity; antimicrobial activity; cancer cell proliferation inhibitory activity condensed tannins; oligomeric flavonoid; synthesis; DPPH radical scavenging activity; antimicrobial activity; cancer cell proliferation inhibitory activity
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Hamada, Y.; Takano, S.; Ayano, Y.; Tokunaga, M.; Koashi, T.; Okamoto, S.; Doi, S.; Ishida, M.; Kawasaki, T.; Hamada, M.; Nakajima, N.; Saito, A. Structure–Activity Relationship of Oligomeric Flavan-3-ols: Importance of the Upper-Unit B-ring Hydroxyl Groups in the Dimeric Structure for Strong Activities. Molecules 2015, 20, 18870-18885.

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