rman structural chemistry OH OH R"=OH R"=OH R.OH ewmidin R=R=OH.robinetinidin Anthocvanidins ocyanidi ed by the ech nus are known as procyanidins chin and techin based polymers yield delphinidin.and the rare mono-substituted flavan-3-based polymers An important group of condensed tannins are 5-deoxy-flavan-3-ols polymers.Branching is common in these tannins,because of the reactivity of the 5-deoxy A ring.Profisetinidins and
Hagerman condensed tannin structural chemistry 4/6 The products of the acid butanol reaction are an unmodified terminal unit, and the colored anthocyanidins produced by the extender units. Catechin- and epicatechin-based polymers produce cyanidin, and thus are known as procyanidins. Gallocatechin and epigallocatechinbased polymers yield delphinidin, and the rare mono-substituted flavan-3-ol based polymers yield pelargonidin. An important group of condensed tannins are 5-deoxy-flavan-3-ols polymers. Branching is common in these tannins, because of the reactivity of the 5-deoxy A ring. Profisetinidins and 5 HO O OH HO O OH OH OH OH OH OH OH 5 O HO OH HO HO OH 5 HO O OH OH OH 5 O OH HO HO OH HO O OH OH OH OH robinetinidol-(4α−>8)-catechin-(6α->4a)-robinetinidol profisetinidin HO O OH R' OH R'' R HO O OH R' R'' R R'' = OH R = R' = H, apigeninidin R = H, R' = OH, luteolinidin Anthocyanidins + + R'' = OH R = R' = H, pelargonidin R = H, R' = OH, cyanidin R = R' = OH, delphinidin R'' = H R = R' = H, guibourtinidin R = H, R' = OH, fisetinidin R = R' = OH, robinetinidin
Hagerman condensed tannin structural chemistry prorobinetinidins comprise the major tannins found in quebracho and acacia tannin preparations. Acid butanol reaction yields the 5-deoxy anthocyanidins fisetinidn and robinetinidin. The acid butanol reaction can be carried out with a nucleophilic trapping agent to produce the terminal unit plus derivitized extender units.These can usually be separated and quantitated by HPLC to give composition and average molecular weight estimates for the parent tannin.Thiols such as toluene-a-thiol are often used in this reaction.but phloroglucinol is more convenient. The efficiency of the reaction with branched condensed tannins,especially the 5-deoxy-flavanol- based tannins has not been established OH HO 0 4B->8 cate OH 2eteialo9egoep Anothe r type of linkage that has been described but not studied extensively involves oxidative C O coupling between the flavonoid rings to yield A2 and related proanthocyanidins. OH epicatechin-()-epicatechin proanthocyanidin A-2
Hagerman condensed tannin structural chemistry 5/6 prorobinetinidins comprise the major tannins found in quebracho and acacia tannin preparations. Acid butanol reaction yields the 5-deoxy anthocyanidins fisetinidn and robinetinidin. The acid butanol reaction can be carried out with a nucleophilic trapping agent to produce the terminal unit plus derivitized extender units. These can usually be separated and quantitated by HPLC to give composition and average molecular weight estimates for the parent tannin. Thiols such as toluene-α-thiol are often used in this reaction, but phloroglucinol is more convenient. The efficiency of the reaction with branched condensed tannins, especially the 5-deoxy-flavanolbased tannins, has not been established. Another type of linkage that has been described but not studied extensively involves oxidative CO coupling between the flavonoid rings to yield A2 and related proanthocyanidins. HO OH OH OH OH O O O OH OH HO OH epicatechin-(2β-->7,4β-->8)-epicatechin proanthocyanidin A-2 HO O OH OH OH OH O O O OH OH OH HO OH OH OH HO OH OH OH OH OH OH HO OH HO OH O OH OH HO OH OH OH OH HO 2 procyanidin epicatechin2 4β−−>8 catechin 2 derivitized extenders + catechin (end group) H+ H+ phloroglucinol (or other nucleophile)
Hagerman condensed tannin structural chemistry The flavan-3,4-diols,or luecoanthocyanidins,are sometimes confused with proanthocyanidins. The flavan-3,4-diols are monomeric flavonoids that yield the anthocyanidins upon treatment with heat and acid.They thus have reactive chemistry similar to that of the condensed tannins,but they do not interact with protein to form precipitable complexes. OH Flavan-3,4-diols R"=H(stable) R=H,R'=OH,leucofisetinidin R"=OH able) R=R opelargonidin R=H,R' OH,leucocyanidin R=R'=OH,leucodelphinidin The flavan-4-ols are also luecoanthoc anidins,but are unique in their lability.They yield the anthocyan din tr upo at山 with alcoholic acid ar HO OH Flavan-4-ols R=H,apiferol(leucoapigeninidin) R=OH,luteoferol(leucoluteolinidin)
Hagerman condensed tannin structural chemistry 6/6 The flavan-3,4-diols, or luecoanthocyanidins, are sometimes confused with proanthocyanidins. The flavan-3,4-diols are monomeric flavonoids that yield the anthocyanidins upon treatment with heat and acid. They thus have reactive chemistry similar to that of the condensed tannins, but they do not interact with protein to form precipitable complexes. The flavan-4-ols are also luecoanthocyanidins, but are unique in their lability. They yield the anthocyanidins upon treatment with alcoholic acid at room temperature. O R'' R' R HO OH OH OH R" = H (stable) R = H, R' = OH, leucofisetinidin R'' = OH (unstable) R = R' = H, leucopelargonidin R = H, R' = OH, leucocyanidin R = R' = OH, leucodelphinidin Flavan-3,4-diols HO O OH OH R OH R = H, apiferol (leucoapigeninidin) R = OH, luteoferol (leucoluteolinidin) Flavan-4-ols
unknown pigment,max=465 nm decays at room temp unknown pigment,max=550 nm OH flavon butanol HCl,cold enaymatcoxidaa R R Stich&Forkmann OH OH HO、 NABH, OH O OH OH aaHpierole2g pigenin) R=OH,luteoferol(e oluteolinidin) max 278 nm H 2 MHCI,heat,15 min R OH HO H' HO、 3-de R.p R=OH 757)yellov 入max 95 cherry red pro-3-deoxyanthocyanidins Stafford has suggested that pro-3-deoxyanthocyanidins might exist in a few plants.Evidence to date is limited to spectroscopy and some chemical conversions that are consi tent with the chemistry shown here.(Stafford,H.A.Flavonoid Metabolism;CRC Press:Boca Raton,FL, 1990,pages65-83). Return to Tannin Chemistry home page. Ann E Hagerman 1998,2002.This material may be copied for use within a single b ned for d on of the author
Stafford has suggested that pro-3-deoxyanthocyanidins might exist in a few plants. Evidence to date is limited to spectroscopy and some chemical conversions that are consistent with the chemistry shown here. (Stafford, H.A. Flavonoid Metabolism; CRC Press: Boca Raton, FL, 1990, pages 65-83). Return to Tannin Chemistry home page. © © Ann E. Hagerman 1998, 2002. This material may be copied for use within a single laboratory but cannot be copied for distribution or publication without permission of the author. HO O OH OH R O HO O OH OH R HO O OH OH R OH HO O OH OH R O HO O OH OH R HO O OH OH R O + enzymatic oxidation (flavone synthase II) Stich & Forkmann NABH4 H+ 2 M HCl, heat, 15 min butanol HCl, cold unknown pigment, λ max = 550 nm H+ flavone R = H, apigenin R = OH, luteolin unknown pigment, λ max = 465 nm decays at room temp 3-deoxy anthocyanidin R = H, apigeninidin λ max = 485 (475?) yellow R = OH, luteolinidin λ max = 495 cherry red flavan-4-ol R =H, apiferol (leucoapigenin) λ max = 275 nm R = OH, luteoferol (leucoluteolinidin) λ max = 278 nm flavanone R = H, naringenin R = OH, eriodictyol pro-3-deoxyanthocyanidins R = H, proapigeninidin R = OH, proluteolinidin
HYDROLYZABLE TANNIN STRUCTURAL CHEMISTRY Ann E.Hagerman ©April14,2002 Hydrolyzable tannins are derivatives of gallic acid(3,4,5-trihydroxyl benzoic acid).Gallic acid is esterified to a core polyol,and the galloyl groups may be further esterified or oxidatively crosslinked to yield more complex hydrolysable tannins. Early work on hydrolyzable tannins included Haslam's significant elucidations of the structures of the simple am,E.Plant enols.Vegetable idge. 1989).M ore recentl atan yza d polyphenols in the emistry of Organi .1-117)have been particula y active in racteri n an fica drolyzable tar ns. etic work (Feldman KS.L of comple awlor MD,and Sahasrab ekeminchemaEotuimiae component coupling strategy for the synthesis of the dimeric ellagitannin coriariin A and a dimeric gallotannin analogue.2000;8011-9)has provided useful insights into likely biosynthetic routes for the complex hydrolyzable tannins.A limited survey of structures and their relationships is provided here. Gallotannins. The simplest hydrolyzable tannins,the gallotannins,are simple polygalloyl esters of glucose The prototypical gallotannin is pentagalloyl glucose(B-1,2,3,4,6-Pentagalloyl-O-D- Gluc se).Pentagalloyl glucose,or PGG.has five identical ester linkages that involve ugar.The alpha anomer is not com OH OH OH OH OH OH OH OH gallic acid O HO OH HO OH B-1,2,3,4,6-pentagalloyl-O-D-glucose
HYDROLYZABLE TANNIN STRUCTURAL CHEMISTRY Ann E. Hagerman © April 14, 2002 Hydrolyzable tannins are derivatives of gallic acid (3, 4, 5-trihydroxyl benzoic acid). Gallic acid is esterified to a core polyol, and the galloyl groups may be further esterified or oxidatively crosslinked to yield more complex hydrolysable tannins. Early work on hydrolyzable tannins included Haslam’s significant elucidations of the structures of the simple gallotannins (Haslam, E. Plant polyphenols. Vegetable tannins revisited, ed.; Cambridge University Press: Cambridge, U. K., 1989). More recently, Okuda et al.(Okuda, T.; Yoshida, T.; Hatano, T. Hydrolyzable tannins and related polyphenols. Progress in the Chemistry of Organic Natural Products 1995, 66, 1-117) have been particularly active in characterization and classification of complex hydrolyzable tannins. Feldman’s synthetic work (Feldman KS, Lawlor MD, and Sahasrabudhe K Ellagitannin chemistry. Evolution of a threecomponent coupling strategy for the synthesis of the dimeric ellagitannin coriariin A and a dimeric gallotannin analogue. 2000; 8011-9) has provided useful insights into likely biosynthetic routes for the complex hydrolyzable tannins. A limited survey of structures and their relationships is provided here. Gallotannins. The simplest hydrolyzable tannins, the gallotannins, are simple polygalloyl esters of glucose. The prototypical gallotannin is pentagalloyl glucose (β-1,2,3,4,6-Pentagalloyl-O-DGlucopyranose). Pentagalloyl glucose, or PGG, has five identical ester linkages that involve aliphatic hydroxyl groups of the core sugar. The alpha anomer is not common in nature. O OH HO OH O O OH OH HO O O OH HO HO O O OH OH OH O O OH OH OH O O OH OH OH OH O β-1,2,3,4,6-pentagalloyl-O-D-glucose gallic acid