Abstract
Ephedra sinica, an important plant in Chinese traditional medicine, contains a complex mixture of proanthocyanidin oligomers as major constituents; however, only the minor components have been chemically characterized. In this study, oligomers with relatively large molecular weights, which form the main body of the proanthocyanidin fractions, were separated by adsorption and size-exclusion chromatography. Acid-catalyzed degradation in the presence of mercaptoethanol or phloroglucinol led to the isolation of 18 fragments, the structures of which were elucidated from their experimental and TDDFT-calculated ECD spectra. The results indicated that (−)-epigallocatechin was the main extension unit, while catechin, the A-type epigallocatechin–gallocatechin dimer, and the A-type epigallocatechin homodimer, were identified as the terminal units. Among the degradation products, thioethers of gallocatechin with 3,4-cis configurations, a B-type prodelphinidin dimer, a prodelphinidin trimer with both A- and B-type linkages, and a prodelphinidin dimer with an α-substituted A-type linkage were new compounds. In addition, a phloroglucinol adduct of an A-type prodelphinidin dimer, a doubly-linked phloroglucinol adduct of epigallocatechin, and a unique product with a flavan-3-ol skeleton generated by the rearrangement of the aromatic rings were also isolated.
Highlights
IntroductionE. sinica, monomeric flavan-3-ols [12,24] and was reportedly induced by the administration of proanthocyanidin oligomers of E. sinica dimeric proanthocyanidins with
Many health benefits of foods and medicinal plants have been attributed to proanthocyanidins [7], and some of their biological activities, including hypotensive and vasorelaxant effects [8,9], improvement of the airway microenvironment in asthma [10], and the inhibition of inflammation and remodeling in murine models of chronic asthma [11], are responsible for the aforementioned activities of E. sinica, especially its respiratory and cardiovascular effects
The proanthocyanidins of E. sinica are mainly composed of oligomers, and in this study, the oligomers were separated and chemically characterized for the first time
Summary
E. sinica, monomeric flavan-3-ols [12,24] and was reportedly induced by the administration of proanthocyanidin oligomers of E. sinica dimeric proanthocyanidins with. Theshown presence of these trimers flavan-3-ols and proanthocyanidins are minor components of thebeen total polyphenol. The degradation involved the cleavage of the proanthocyanidin by acid-catalyzed degradation in the presence of nucleophilic agents, interflavan bonds oligomers under acidic conditions, generating flavan-3-ols from the terminal units and interflavan bonds from under acidic conditions, generating flavan-3-ols from the terminal units and that is, 2-mercaptoethanol or phloroglucinol. The degradation involved the cleavage of the Flavanyl-4 cations from the extension units, which were trapped by nucleophilic agents
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