Tannins precursors

Chalcones (e.g., 9) are key intermediates in the formation of several major groups of flavonoids (see Fig. 11.2). In some plants, they are converted into aurones (such as 11). In other instances, chalcones undergo reduction of the exocy-clic double bond to produce dihydrochalcones (such as 12). Chalcones and flavanones (e.g., 10) exist in equilibrium in in vitro systems. However, as only flavanones with a (25)-configuration are known to occur naturally, this interconversion appears to be enzymatically controlled and does not involve racemization. Desaturation of flavanones can yield flavones (such as 4 and 5), whereas introduction of oxygen at the 3-position gives dihydroflavonols (flavanonols) (such as 13) which, in turn, are the precursors of flavonols (e.g., 6-8), anthocyanins (e.g., 1-3), and condensed tannin precursors (Ebel and H lbrock, 1982 Hahlbrock, 1981 Haslam 1974) (Figs. 11.7 and 11.8). 

Drewes S E, Roux D G 1964 Condensed tannins. 18. Stereochemistry of flavan-3,4-diol tannin precursors (+)-mollisacacidin, (-)-leucofisetinidin and (+)-leucorobinetinidin. Biochem J 90 343-350... 

VII. Composition of the Metabolic Pool and Condensation Aptitudes of Tannin Precursors... 

Infinitely more complex is the metabolic composition represented in the woods of the black wattle (A. mearnsii) and of many related Australian and South African Acacia species [e. g. in the sections Brunioideae and Uninerves 23)]. Notable is the dominance of (-h)-leucofisetinidin [( + )-mollisacacidin] as putative electrophilic tannin precursor and the complete absence of (+ )-catechin as nucleophilic substrate amongst the metabolites. The metabolitic pool is populated by four unique biflavanoids with terminal 3,4-diol function (Scheme 14) and a linear [4,6 4,6]-triflavanoid homologue, as well as a complete series of four angular [4,6 4,8]-triflavanoids each with a centrally incorporated (-h )-catechin unit (Scheme 14). Here the plausible interpretation is that (+)-catechin, when available at low concentration in an otherwise weakly nucleophilic (but excessively electrophilic) environment is immediately and quantitatively converted into... 

Although flavor precursors in the unroasted cocoa bean have no significant chocolate flavor themselves, they react to form highly flavored compounds. These flavor precursors include various chemical compounds such as proteins, amino acids, reducing sugars, tannins, organic acids, and many unidentified compounds. 

Flavan-3,4-diols FIavan-3,4-diols, also known as leucoanthocyanidins, are not particularly prevalent in the plant kingdom, instead being themselves precursors of flavan-3-ols (catechins), anthocyanidins, and condensed tannins (proanthocyanidins) (see Fig. 5.4). Flavan-3,4-diols are synthesized from dihydroflavonol precursors by the enzyme dihydroflavonol 4-reductase (DFR), through an NADPH-dependent reaction (Anderson and Markham 2006). The substrate binding affinity of DFR is paramount in determining which types of downstream anthocyanins are synthesized, with many fruits and flowers unable to synthesize pelargonidin type anthocyanins, because their particular DFR enzymes cannot accept dihydrokaempferol as a substrate (Anderson and Markham 2006). 

This technique has been applied to the determination of organic compounds and cations including crude oils, fulvic acids, tannins, carbohydrates, trihalomethane precursors and lithium. 

The high loading capability of large-volume CCC systems is commonly used in industry. Large amounts (gram to kilogram scale) of natural products with high added values are separated by CCC. Alkaloids, antibiotics, enzymes, macrolides, peptides, rare fatty acids, saponins, tannins, taxoids and/or precursors of Taxol , and other fine chemicals have been isolated, separated, and/or purified by preparative CCC [1]. 

Use Dyes intermediates benzyl compounds synthetic tannins perfumery pharmaceuticals manufacture of photographic developer gasoline gum inhibitors penicillin precursors quaternary ammonium compounds. 

The nature of the structure depends on the assumptions one uses as to the probable precursors for the humate. Lignin is a favorite precursor others include tannins, quinones, microbiological metabolites, sugar-amine condensation products, and other products (Stevenson, 1982). 

From carbohydrate precursors there is another biosynthetic pathway to shikimic acid and further to gallic acid and tannins. Shikimic acid is the starting material, via chorismic acid (formed by reaction with a second molecule of pyruvic acid) which gives rise to aromatic, i.e. phenolic, amino acids. 

In conclusion, it is heartening to witness the lively rebirth of tannins as precursors of promising materials. As with other natural monomers and macromonomers, it appears that the possible interest of polymer bioprocesses could also be assessed on tannins, a type of study that has not been published thus far. 

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