Chemistry and Significance of Condensed Tannins by Herbert L. Hergert (auth.), Richard W. Hemingway, Joseph J.

By Herbert L. Hergert (auth.), Richard W. Hemingway, Joseph J. Karchesy, Susan J. Branham (eds.)

This ebook used to be built from the court cases of the 1st North American Tannin convention held in Port. Angeles, Washington, August 1988. the target of the convention used to be to assemble individuals with a standard curiosity in condensed tannins and to advertise interdisciplinary interactions that would bring about a greater figuring out of those vital ingredients. Anot. her goal was once the publicat. ion of this e-book simply because there has now not been a monograph dedicated to the chemistry and value of tannins for a number of many years. The booklet is geared up into sections facing the biosynthesis, constitution, re­ activities, complexation with different biopolymers, organic value, and use of tannins as strong point chemical substances. The authors made a distinct try to specialise in what we do not comprehend in addition to to supply a precis of what we do be aware of to be able to help in making plans destiny learn. Our thank you visit the authors who so kindly contributed chapters and so pa­ tiently spoke back to our requests. We additionally thank Rylee Geboski and the convention help. ance employees, university of Forestry, Oregon country college, for his or her guidance in making plans and engaging in t. he convention, and Julia Wilson, Debbie Wolfe, Helen Coletka, and Nancy Greene of the Southern woodland scan Station, Pineville, Louisiana, who typed the chapt. ers. Linda Chalker-Scott was once specially priceless in helping us wit. h modifying. Dick Hemingway is indebted t. o the employees of the Alexandria Forest.

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1s 5. 3H-phenylalanine- retention of H that is on C-2 of proanthocyanidin unit, but loss at C_3. 7,19 By the action of 4-coumarate:CoA ligase, the p-coumarate is converted to the CoA ester 20 ,21 that is required to form the B- and C-rings of the flavonoid unit. The malonyl CoA required to form the A-ring is synthesized from acetyl-CoA and HC03- by acetyl-coenzyme A:bicarbonate ligase. 22 ,23 Lewis discusses the pre-C-15 level in more detail in Chapter 2. Chalcone Synthase and Isomerase to Form Flavanones The first C-15 intermediate of flavanoids with a 5,7-dihydroxy A-ring is naringenin chalcone, an open-chain flavonoid with a p-hydroxy B-ring formed by the condensation of 3 malonyl-CoA molecules with p-coumaroyl-CoA, via chalcone synthase 7,l1 (Figures 1 and 2).

In the initial work of Neish's laboratory in 1957,10 the dual aspects of the pathway were demonstrated by showing that all of the carbons of 14C-Iabeled phenylalanine were incorporated into the Band C-rings, whereas, the acetate carbons of malonyl Co-A were conserved in the A-ring of the C-15 flavonoid molecule 7,1l (Figure 1). In 1970, it was shown that the hydrogen at the appropriate carbon of the chalcone was directly transferred to the C-3 of the flavanone. 12 In 1973, labeled phenylalanine and dihydrokaempferol (the stereochemistry was not reported) fed to tea plants were incorporated into ( - )-epicatechin.

Note also the pendant gallic acid residues in structure (36) linking the biogenetic pathways between hydrolyzable and condensed tannins. These structural variations are discussed in more detail by Hemingway in Chapter 5 of this volume. In proanthocyanidins, the flavonoid skeleta can readily be divided into two broad categories, namely, those containing either phloroglucinol or resorcinol (so-called 5deoxy) substitution patterns (Figure 5). These broad categories can also be further subdivided into individual families depending upon the degree of hydroxylation in either the "B" ring or at C-3.

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