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• 29106-49-8 procyanidin B₂ 
• 108-24-7 acetic anhydride 

Relevant academic research and scientific papers

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]

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.

A New Investigation of Tiliae flos DAB 8

The isolation and structure elucidation of two dimeric proanthocyanidins Tiliae flos DAB 8 is described.

Bioassay-Guided fractionation of a leaf extract from combretum mucronatum with anthelmintic activity: Oligomeric procyanidins as the active principle

Combretum mucronatum Schumach. & Thonn. is a medicinal plant widely used in West African traditional medicine for wound healing and the treatment of helminth infections. The present study aimed at a phytochemical characterization of a hydroalcoholic leaf extract of this plant and the identification of the anthelmintic compounds by bioassay-guided fractionation. An EtOH-H2O (1:1) extract from defatted leaves was partitioned between EtOAc and H2O. Further fractionation was performed by fast centrifugal partition chromatography, RP18-MPLC and HPLC. Epicatechin (1), oligomeric proanthocyanidins (OPC) 2 to 10 (mainly procyanidins) and flavonoids 11 to 13 were identified as main components of the extract. The hydroalcoholic extract, fractions and purified compounds were tested in vitro for their anthelmintic activity using the model nematode Caenorhabditis elegans. The bioassay-guided fractionation led to the identification of OPCs as the active compounds with a dose-dependent anthelmintic activity ranging from 1 to 1000 μM. Using OPC-clusters with a defined degree of polymerization (DP) revealed that a DP ≥ 3 is necessary for an anthelmintic activity, whereas a DP > 4 does not lead to a further increased inhibitory effect against the helminths. In summary, the findings rationalize the traditional use of C. mucronatum and provide further insight into the anthelmintic activity of condensed tannins.

Proanthocyanidins and a phloroglucinol derivative from Rumex acetosa L.

From the ethyl acetate soluble fraction of an acetone-water extract of the aerial parts of Rumex acetosa L. (Polygonaceae), a variety of monomeric flavan-3-ols (catechin, epicatechin, epicatechin-3-O-gallate), A- and B-type procyanidins and propelargonidins (15 dimers, 7 trimers, 2 tetramers) were isolated with 5 so far unknown natural products. Dimers: procyanidin B1, B2, B3, B4, B5, B7, A2, epiafzelechin-(4β→8)-epicatechin, epiafzelechin-(4β→8)-epicatechin-3-O-gallate (new natural product), epiafzelechin-(4β→6)-epicatechin-3-O-gallate (new natural product), epiafzelechin-3-O-gallate-(4β→8)-epicatechin-3-O-gallate, B2-3′-O-gallate, B2-3,3′-di-O-gallate, B5-3′-O-gallate, and B5-3,3′-di-O-gallate. Trimers: procyanidin C1, epiafzelechin-(4β→8)-epicatechin-(4β→8)-epicatechin (new natural product), epicatechin-(4β→8)-epicatechin-(4β→8)-catechin, cinnamtannin B1, cinnamtannin B1-3-O-gallate (new natural product), tentatively epicatechin-(2β→7, 4β→8)-epiafzelechin-(4α→8)-epicatechin (new natural product), and epicatechin-3-O-gallate-(4β→8)-epicatechin-3-O-gallate-(4β→8)-epicatechin-3-O-gallate. Tetramers: procyanidin D1 and parameritannin A1. All compounds were elucidated by ESI-MS, CD spectra, 1D- and 2D-NMR experiments as free phenols or peracetylated derivatives and, in part, after partial acid-catalysed degradation with phloroglucinol. A more abundant proanthocyanidin polymer was also isolated, purified and its chemical composition studied by 13C NMR. In addition a so far unknown phloroglucinolglycoside (1-O-β-d-(2,4-dihydroxy-6-methoxyphenyl)-6-O-(4-hydroxy-3,5-dimethoxybenzoyl)-glucopyranoside) was isolated.

Synthetic studies of proanthocyanidins. Part 5.1 Highly stereoselective synthesis and inhibitory activity of Maillard reaction of 3,4-trans catechin and epicatechin dimers, procyanidin B1, B2, B3, B4 and their acetates

TMSOTf-catalyzed condensation of a potential electrophile with a nucleophile was achieved with a high level of 3,4-trans condensation, and we succeeded in the stereoselective synthesis of procyanidin B2 and its peracetate. Studies on the inhibitory activity of the Maillard reaction of four 3,4-trans series of catechin and epicatechin dimers, procyanidin B1, B2, B3 and B4, and their peracetates were also carried out.

PROCYANIDINS AND POLYPHENOLS OF LARIX GMELINI BARK

Key Word Index - Larix gmelini; Pinaceae; bark; catechins; procyanidins; biflavonoids; larixinol.Methanol extracts of Larix gmelini bark yielded (-)-epiafzelechin, (+)-catechin and (-)-epicatechin, dimeric procyanidins B-1, B-2, B-3 and B-4 and oligomeric procyanidins.Chemical degradation of the oligomers using toluene-α-thiol and acetic acid showed the oligomers to have flavan-3-ol terminal units possessing either the 2,3-trans (catechin) or 2,3-cis (epicatechin) stereochemistry, with the former predominating.Likewise the extension units were shown to consist of flavan-3-ol units with 2,3-trans or 2,3-cis stereochemistry in roughly equal proportion.The average degree of oligomerization was calculated as 6-7 and the number average molecular weight as 1700-2000.The structure of the residual procyanidins remaining in the bark after methanol extraction is also briefly commented upon.Larixinol is shown to have an unusual spirobiflavonoid structure and a pathway of biogenesis is proposed.

SYNTHESIS AND CHARACTERIZATION OF PROCYANIDIN DIMERS AS THEIR PERACETATES AND OCTAMETHYL ETHER DIACETATES

Key Word Index - Biomimetic synthesis; procyanidins B1-B8; 3,4-cis-biflavanoid; all--bi--(+)-catechin; 1H NMR parameters. Condensation of (2R,3S,4R or S)-leucocyanidin or the 5,7,3',4'-tetramethyl ether of (2R,3R,4S)-leucocyanidin with flavan-3-ols yielded dimeric flavanoids which were converted to their octamethyl ether diacetates, or the deca-acetates for the 2,3-trans-procyanidin series.Comparison is made of the 1H NMR spectra of the deca-acetate and octamethyl ether diacetate derivatives which lead to useful diagnostic shift parameters characteristic of their structures.Condensation afforded a novel biflavanoid with a 3,4-cis-configuration and a triflavanoid of 'mixed' stereochemistry.

Synthesis and Conformation of Procyanidin Diastereoisomers

The four theoretically possible diastereoisomeric 4->8 linked procyanidin dimers with two 2,3-cis-flavanoid units, epicatechin-(4β->8)-epicatechin (6), epicatechin-(4β->8)-ent-epicatechin (8), ent-epicatechin-(4α->8)-epicatechin (7), and ent-epicatechin-(4α->8)-ent-epicatechin (2), have been synthesized together with the 2,3-trans diastereoisomers catechin-(4α->8)-catechin (14) and catechin-(4α->8)-ent-catechin (15).The preferred rotamer conformations of the deca-acetate derivatives of (6), (8), (14), and (15) in chloroform were deduced from their 13C n.m.r. and high-field 1H n.m.r. spectra.The 1H n.m.r. spectra of the preferred conformers of the pairs of acetate derivatives of (6) and (15), and (8) and (14), were qualitatively similar as the relative configuration about the interflavanoid bond of one pair has a meso-relationship to the other.

DIMERIC FLAVANOLS OF Juniperus sabina. I.

Procyanidins B2, B3, and B4 have been isolated from Juniperus sabina for the first time.On the basis of chemical transformations and the PMR spectroscopy of their decaacetates, and absolute configurations of the asymetric centers of each of the halves of the molecules of the dimer have been determined: 2R, 3R, 4R for the "upper" half and 2R, 3R for the "lower" half of B2, 2R, 3S, 4S for the "upper" half and 2R, 3S, for the "lower" half of B3; and 2R, 3S, 4S for the "upper" half and 2R, 3R for the "lower" haalf of B4.