Recent epidemiological research indicates that diets rich in flavonoid-containing foods may be associated with a reduced risk for cardiovascular disease. This protective effect is attributed, in part, to the ability of flavonoids to act as antioxidants. Certain chocolates and cocoas contain substantial amounts of procyanidins, and thus belong in the category of flavonoid-rich foods. Recent advancements in the identification and isolation of procyanidins, especially oligomeric procyanidins, from chocolate and cocoa have facilitated the investigation of individual procyanidin fractions with regard to their potential cardiovascular health benefits. In the following paper, we report on the antioxidant capacity of a cocoa as determined by the Oxygen Radical Absorbance Capacity (ORAC) assay, and the ability of individual procyanidin fractions from this same cocoa to inhibit low-density lipoprotein (LDL) oxidation in vitro. In addition, mechanisms are discussed by which flavonoids in chocolate and cocoa may enhance cardiovascular health.
Browse Scientific Research by Journal
In the current study, we investigated the usefulness of reversed-phase and normal-phase chromatography for comparing the separation of low molecular weight flavonoids in green tea versus the oligomeric procyanidins in cocoa. The results of this study demonstrated that the reversed-phase technique was better suited for the separation of the flavan-3-ols and flavonols in green tea while the normal-phase method was superior for separation of flavan-3-ol oligomers in cocoa. Therefore, it was concluded that both techniques are required for a comprehensive survey of the flavonoid classes that are ubiquitous in nature.
A project has been initiated to synthesize proanthocyanidin oligomers found in cocoa. Natural, readily available (+)-catechin was transformed into 5,7,3‘,4‘-tetra-O-benzyl-(−)-epicatechin (14) by (a) benzylation of the phenolic oxygens; (b) oxidation of the 3-alcohol to ketone by the Dess−Martin periodinane; and (c) reduction with lithium tri-sec-butylborohydride (l-Selectride) in the presence of LiBr. The additive diminishes the extent of ketone enolization while maintaining a stereoselectivity of ≥200:1. Oxidation of 14 with DDQ was performed best from the standpoint of product purification if ethylene glycol was used as the nucleophilic trapping agent. The resulting ether 19 was condensed with 14 using TiCl4 to give a good yield of benzyl-protected epicatechin-4β,8-epicatechin (octa-O-benzylprocyanidin B2, 20) as the sole dimeric product. Hydrogenolysis of 20 yielded procyanidin B2 in the first enantiospecific synthesis of this natural product which employs protected intermediates and thereby allows the necessary product separation after the condensation step to be performed on nonpolar, nonsensitive intermediates. Acylation of 20 with tri-O-benzylgalloyl chloride followed by hydrogenolysis gave access to the title bis-gallate (24). This constitutes the first synthesis of this natural product, a compound notable for its PKC-inhibitory and anticancer activity.
