Type -B procyanidins

Quantitative data for chocolate are limited, but the available literature demonstrates that it is a good potential source of (+)-catechin, (-)-epicatechin, and type B procyanidins. Dark chocolate, for example, contains 6.6 mg, 21.8 mg, and 2.1 mg/100 g of catechin epicatechin, and procyanidins, respectively. 

Type-B procyanidins (C30H26O12) (Figure 6.15) are dimers resulting from the condensation of... 

Type-A procyanidins (C30H24O12) (Figure 6.16) are dimers that, in addition to the C4-C8 or C4-C6 interfiavan bond, also have an ether bond between the C5 or C7 carbons of the terminal unit and the C2 carbon of the upper unit. Procyanidin A2 has been identified in wine (Vivas and Glories, 1996). Form B can change to form A via a radical process. 

Fig. 6.15. Structure and schedule of type-B dimeric procyanidins (de Freitas, 1995)...

Type-C procyanidins are trimers with two interflavan bonds corresponding to those of type-B dimers. 

The B-type procyanidins include a mixture of oligomers and polymers composed of flavan-3-ol units linked mainly through C4 C8 and/or C4 C6 bonds, and represent the dominant class of natural proanthocyanidins. Among the dimers, procyanidins Bl, B2, B3 and B4 (Fig. 2a) are the most frequently occurring in plant tissues. Procyanidin B5 (EC-(4j6 6)-EC), B6 (catechin-(4o 6)-catechin), B7 (EC-(4/3 6)-catechin) and B8 (catechin-(4q 6)-EC) are also widespread (Eig. 2b) [17-19]. 

The A-type proanthocyanidins are characterized by a second ether linkage between an A-ring hydroxyl group of the lower unit and C-2 of the upper unit. Since they are less frequently isolated from plants than the B-types, they have been considered unusual structures [18,19]. The first identified A-type proanthocyanidin was procyanidin A2 isolated from the shells of fruit of Aes-culus hippocastanum. Since then, many more A-type proanthocyanidins have been found in plants, including dimers, trimers, tetramers, pentamers and ethers [18,21]. 

Liu L, Xie B, Cao S, Yang E, Xu X and Guo S. 2007. A-type procyanidins from Lit chi chinensis pericarp with antioxidant activity. Food Chem 105 1446—1451. 

Sun, W. and Miller, J.M., Tandem mass spectrometry of the B-type procyanidins in wine and B-type dehydrodicatechins in an autoxidation mixture of (+)-catechin and (-)-epicatechin, J. Mass Spectrom., 38, 438, 2003. 

X-ray and CD analysis. The structure of procyanidin B-1 was unequivocally confirmed by x-ray analysis of its deca-(9-acetyl derivative by Weinges, one of the pioneers in the field of proanthocyanidin chemistry. One of the most powerful methods to establish the absolute configuration at C-4 of the T-unit in dimeric A- and B-type proanthocyanidins remains the chiroptical method via application of the aromatic quadrant rule. This has been repeatedly demonstrated by the author s own work and several other contributions listed in Refs. 7-12. 

Kozikowski, A.P., Tuckmantel, W., and Hu, Y., Studies in polyphenol chemistry and bioactivity. 3. Stereocontrolled synthesis of epicatechin-4a,8-epicatechin, an unnatural isomer of the B-type procyanidins, J. Org. Chem., 66, 1287, 2001. 

Kondo, K. et al.. Conversion of procyanidin B-t5 pe (catechin dimer) to A-type evidence for abstraction of C-2 hydrogen in catechin during radical oxidation, Tetrahedron Lett., 41,485, 2000. 

Prototypes (1) to (3) possess resorcinol-type flavanyl units attached to (-b)-catechin or (+)-gallocatechin, whereas, procyanidin prototypes (4a) are uniformly based on phloroglucinol-type flavanyl units. 

Cranberries have been used traditionally for the treatment and prevention of urinary tract infections. Their effectiveness was demonstrated by a randomized, double-blind placebo-controlled trial (Avom et ah, 1994). Escherichia coli are the principal bacterial species responsible for urinary tract infection. The consumption of cranberry juice reduced the adherence of E. coli to the uroepithelial bladder cells in healthy human volunteers (Di Martino et ah, 2006). A-type procyanidin dimers and trimers that were isolated from cranberries were found to inhibit the adherence of uropathogenic E. Coli, whereas (—)-epicatechin and a B-type dimer were not effective (Foo et ah, 2000). 

Proanthocyanidins with one A-type linkage have two less hydrogen than those of the B-type proanthocyanidins. A procyanidin trimer gave rise to [M-H] m/z 865, whereas a procyanidin trimer with one-type linkage yielded [M H] m/z 863. A-type interflavan bond differs from B-type bound in that they do not undergo QM cleavage. Thus,... 

Procyanidins are plant phenolic compounds found in several plant species. They may be present as monomers or as oligomers (tannins). Two linkage types are possible in A-type procyanidins both C-C and ether bonds are formed, while in the B-type only C-C bonds are formed, either via 4 6 or 4 8 hnks. The LC-MS of B-type procyanidins is reported most frequently. 

The B- and A-type procyanidins and proanthocyanidins (condensed or nonhydrolyzable tannins, Fig. 6.4) are polymers of flavan-3-ols present in the skin and seeds of the grape berry. In winemaking, they are transferred to the wine, and the sensorial characteristics of astringency and bitterness of wine are linked to the galloylation degree (DG) and degree of polymerization (PD) of flavan-3-ols (Cheynier and Rigaud, 1986 Vidal et al., 2003). 

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