256236-21-2Relevant articles and documents
An improved synthesis of procyanidin dimers: Regio- and stereocontrol of the interflavan bond
Tarascou, Isabelle,Barathieu, Karine,Andre, Yann,Pianet, Isabelle,Dufourc, Erick J.,Fouquet, Eric
, p. 5367 - 5377 (2007/10/03)
A direct and general synthesis of procyanidin dimers B1, B2, B3 and B4 (10a-d) is presented. The approach is based on the stoichiometric coupling of two protected monomeric units (the nucleophilic 2a-b and electrophilic 4a-b partners) and deals with the regio- and stereocontrol of the C4-C8 interflavan bond as well as the control of the degree of oligomerization. The synthesis involves a five-step pathway starting from the native catechin (1a) or epicatechin (1b) to the fully deprotected dimers 10a-d. Furthermore, the process appears to be iterative as the coupling intermediates 9a-d themselves can be readily used in further selective syntheses of trimers or higher oligomers. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
Studies in polyphenol chemistry and bioactivity. 1. Preparation of building blocks from (+)-catechin. Procyanidin formation. Synthesis of the cancer cell growth inhibitor, 3-O-galloyl-(2R,3R)-epicatechin-4β,8-[3-O-galloyl-(2R,3R)-epicatechin]
Tueckmantel, Werner,Kozikowski, Alan P.,Romanczyk Jr., Leo J.
, p. 12073 - 12081 (2007/10/03)
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.
