Prodelphinidin units

The designations cis and trans relative to the procyanidin and prodelphinidin units indicate the... 

Another concern has been that the hydroxylation patterns of the dihydro-flavonols and flavonols are often not reflected in the co-occurring proanthocyanidins. In the barks of southern pines for example, dihydromyricetin and myricetin are prominent constituents of the outer bark (151). However, the proanthocyanidins and condensed tannins have only very small proportions of prodelphinidin units (146). It is probable that the pool of dihydro flavonols used in reduction to flavan-3,4-diols and flavan-3-ols occurs prior to the hydroxylation at C-5. ... 

The presence of propelargonidin units (1, 4) in a polymer is also very readily detected as the 4 -hydroxy B-ring possesses a two-carbon signal at <5 129 (C-2 and C-6 ), which is quite separate from any signals from procyanidin or prodelphinidin units (29). 

Specific rotation in water c = catechin e = epicatechin egc = Procyanidin units Prodelphinidin units... 

ESI-MS in the positive ion mode enabled to detect [M + H] ions up to the galloylated pentamer. Analysis of wine proanthocyanidins showed the presence of additional series of species with 16 mass unit differences to signals given by grape seed procyanidins. These were attributed to the presence of (epi)gallocatechin units in mixed procyanidin prodelphinidin... 

As discussed above, the development of mild MS techniques has led to further progress in the determination of proanthocyanidin size distribution. In particular, ESI-MS studies have demonstrated that prodelphinidin and procyanidin units coexist within the polymers, where they seem distributed at random. A list of mass signals attributed to proanthocyanidins detected in grape or wine extracts is given in Table 5.2. 

Foo, L. and Porter, L., Prodelphinidin polymers definition of structural units. J. Chem. Soc. Perkin Trans. /1186, 1978. 

To analyze proanthocyanidins, this unit relies on the susceptibility of the proanthocyani-din interflavonoid bond to acid catalysis. Interflavonoid bonds have different susceptibilities to acid catalysis (Hemingway and McGraw, 1983 Beart et al., 1985). In general, and for procyanidins and prodelphinidins, subunits that are bonded through the benzylic position (C4) are susceptible to acid catalysis. Most natural proanthocyanidins extracted from plant tissue have this type of interflavonoid bond and are therefore suitable candidates for this analytical technique. 

The most abundant type of proanthocyanidins in plants are the procyani-dins, which consist exclusively of (epi)catechin units. The less common proanthocyanidins containing (epi)afzelechin (Fig. 1.11) and (epi)gallocatechin (Fig. 1.10) subunits are called propelargonidins and prodelphinidins, respectively [Balentine et al., 1997]. 

Probably mainly as the result of a more uniform mass distribution and with considerable emphasis on lower mass units, prorobinetinidins and profisetinidins (1) to (3) occur in mixtures that are more readily water-soluble than those of procyanidins (4a) and prodelphinidins (4b). However, oxidative effects as the result of weathering of barks may also play a role in reducing the solubility of the latter group. 

Several proanthocyanidin classes can be distinguished on the basis of the hydroxylation pattern of the constitutive units. Among them, procyanidins, consisting of (epi)catechin units (3, 4 di OH), and prodelphinidins, deriving from (epi)gallocatechin (3 ,4, 5 tri OH), Figure 2, have been reported in grapes. 

The B-ring substitution pattern influences the absorbance. Pure prodelphinidin polymers show much lower specific absorption coefficients (El% = 62) than pure procyanidin polymers (E 0/o = 130) [141]. The molar absorption coefficients of dimeric and higher oligomeric procyanidins are similar (see Tab. (8)). The overall UV absorbance of an oligomer approximately amounts to the sum of the absorbances of the monomer units [226,254], However, UV detection of individual procyanidins after chromatographic separation implies that - in this case - molar absorbances depend on structure. In the series (+)-catechin, procyanidin B2, Cl and a tetramer molar absorbances decreased [262], Treutter et al. [154] found lower molar absorbances for dimers with a 2,3-cis stereochemistry (procyanidin B2 and B5) compared to (-)-epicatechin and (+)-catechin which nearly showed identical molar calibration plots. The molar absorbance of the doubly-linked procyanidin A2 was much higher than the ones of the monomers. 

The most important members, however, are proanthocyanidin polymers, also called nonhydrolyzable or condensed tannins. Proanthocyanidin polymers exist as chains of C-4-C-8 (or C-6) linked flavan-3-ol units (Fig. 318). The monomer unit may be based on either of two stereochemistries designated as cis and trans and on either of two B-ring hydroxylation patterns, the procyanidin (PC) and the prodelphinidin (PD) units. Thus the polymer chains are characterized by the average stereochemistry and the PC PD ratios (Table 56). 

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