Abstract
In 1990, Okuda et al. reported the first isolation and characterization of oenothein B, a unique ellagitannin dimer with a macrocyclic structure, from the Oenothera erythrosepala leaves. Since then, a variety of macrocyclic analogs, including trimeric–heptameric oligomers have been isolated from various medicinal plants belonging to Onagraceae, Lythraceae, and Myrtaceae. Among notable in vitro and in vivo biological activities reported for oenothein B are antioxidant, anti-inflammatory, enzyme inhibitory, antitumor, antimicrobial, and immunomodulatory activities. Oenothein B and related oligomers, and/or plant extracts containing them have thus attracted increasing interest as promising targets for the development of chemopreventive agents of life-related diseases associated with oxygen stress in human health. In order to better understand the significance of this type of ellagitannin in medicinal plants, this review summarizes (1) the structural characteristics of oenothein B and related dimers; (2) the oxidative metabolites of oenothein B up to heptameric oligomers; (3) the distribution of oenotheins and other macrocyclic analogs in the plant kingdom; and (4) the pharmacological activities hitherto documented for oenothein B, including those recently found by our laboratory.
Highlights
Antioxidant polyphenols in medicinal plants, foods, and fruits are currently acknowledged as important beneficial constituents that reduce the risk of life-related diseases closely associated with active oxygen damage, such as cancers, arteriosclerosis, diabetes, and coronary heart diseases, and have been explored as plausible chemopreventive agents for the human healthcare market.Polyphenols have received increasing attention for the discovery and development of their new physiological functions
In contrast to condensed tannins and gallotannins (Turkish or Chinese gall), which were long recognized in the leather industry [1], ellagitannins in medicinal plants had been little studied before the discovery of geraniin (1) from a Japanese folk medicine, Geranium thunbergii (Geraniaceae), by Okuda’s group in 1976 [2,3]
This review provides a better understanding of the significance of those antioxidant tannin constituents in medicinal plants, which may lead to future developments of preventive or therapeutic agents for various chronic diseases associated with oxygen stress by active oxygen species and free radicals
Summary
Antioxidant polyphenols in medicinal plants, foods, and fruits are currently acknowledged as important beneficial constituents that reduce the risk of life-related diseases closely associated with active oxygen damage, such as cancers, arteriosclerosis, diabetes, and coronary heart diseases, and have been explored as plausible chemopreventive agents for the human healthcare market. In contrast to condensed tannins and gallotannins (Turkish or Chinese gall), which were long recognized in the leather industry [1], ellagitannins in medicinal plants had been little studied before the discovery of geraniin (1) from a Japanese folk medicine, Geranium thunbergii (Geraniaceae), by Okuda’s group in 1976 [2,3]. This review summarizes the structural characteristics of oenothein B (4) and related oxidized metabolites, up to heptameric oligomer, found in medicinal plants and their diverse biological functions hitherto reported, including those discovered recently in our laboratory. This review provides a better understanding of the significance of those antioxidant tannin constituents in medicinal plants, which may lead to future developments of preventive or therapeutic agents for various chronic diseases associated with oxygen stress by active oxygen species and free radicals
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