TANNINSTANNINS

M. Ahsan Khalid, M. Ahsan Khalid, B.PharmB.Pharm, Pharm. D, Pharm. DM.PhilM.Phil Scholar (RIPS/RIU)Scholar (RIPS/RIU)

HIPSHIPS--HUKICHUKIC

PHARM. DChemical Pharmacognosy- I

Lecture 30 May 16th, 2011

1. Tannins are secondary metabolites of 1. Tannins are secondary metabolites of plants, nonplants, non--nitrogenous, nitrogenous, phenolicphenolic in in nature. nature.

2. They have a property to tan animal skin 2. They have a property to tan animal skin to convert to leather or hide. to convert to leather or hide.

3. Conversion imparts resistance to water, 3. Conversion imparts resistance to water, heat, abrasives. heat, abrasives.

4. They can be extracted using water4. They can be extracted using water--acetone/alcohol mixture. acetone/alcohol mixture.

5. They have a property to precipitate 5. They have a property to precipitate gelatin & heavy metals. gelatin & heavy metals.

Tannins: IntroductionTannins: Introduction

Tannins: IntroductionTannins: IntroductionTannins: pale yellow to light brownTannins: pale yellow to light brown--red amorphous substances widely red amorphous substances widely

distributed in plants and used chiefly in tanning leather, dyeing distributed in plants and used chiefly in tanning leather, dyeing fabric, and making ink.fabric, and making ink.

Their solutions are acid and have an astringent taste.Their solutions are acid and have an astringent taste.

They are isolated from oak bark, sumac, and galls.They are isolated from oak bark, sumac, and galls.

Tannins give tea astringency, Tannins give tea astringency, colourcolour, and , and flavourflavour. .

Tannins are used industrially to clarify wine and beer, reduce viscosity Tannins are used industrially to clarify wine and beer, reduce viscosity of oilof oil--well drilling mud, and they have also had medical useswell drilling mud, and they have also had medical uses

Tannins are mainly found in the cell vacuoles or in the cuticle (here Tannins are mainly found in the cell vacuoles or in the cuticle (here cells don’t interfere with plant processes: only after death and cell cells don’t interfere with plant processes: only after death and cell breakdown so they become active in metabolic processes). breakdown so they become active in metabolic processes).

Tannins are Tannins are phenolicphenolic glycosides.glycosides.

TANNINSTANNINS Historically, the importance of tanninHistorically, the importance of tannin--containing drugs is containing drugs is

linked to their tanning properties (ability to transform linked to their tanning properties (ability to transform fresh hides into leather). fresh hides into leather).

Today, tanning is achieved with mineral compounds, but Today, tanning is achieved with mineral compounds, but for several millennia, it had required exclusively the used for several millennia, it had required exclusively the used of plant products. of plant products.

These included chestnut tree tannin (These included chestnut tree tannin (CastaneaCastanea sativasativaL.), oak tannin (L.), oak tannin (QuercusQuercus robarrobar L) in Europe, but also, in L) in Europe, but also, in other parts of the world, tannins from other parts of the world, tannins from AnacardiaceaAnacardiacea((QuebrachoQuebracho –– SchinopsisSchinopsis sppspp), sumacs (), sumacs (RhusRhus sppspp), ), Legumes (acacias Legumes (acacias –– Acacia Acacia sppspp) or ) or CombretaceaeCombretaceae((myrobalansmyrobalans –– TerminaliaTerminalia sppspp). ).

Some of these tannins are still prized for leathers Some of these tannins are still prized for leathers designed for specific uses (fine leather products).designed for specific uses (fine leather products).

Tannins Tannins -- TanningTanningThe consequence of tanning: formation of bonds The consequence of tanning: formation of bonds

between the collagen fibres of the hide (imparts between the collagen fibres of the hide (imparts resistance to water, heat and abrasionresistance to water, heat and abrasion.).)

This capability of tannins to combine with This capability of tannins to combine with macromolecules explains why they precipitate macromolecules explains why they precipitate cellulose, pectins and proteins; it also explains cellulose, pectins and proteins; it also explains their characteristic their characteristic astringencyastringency and tartness: by and tartness: by precipitating the glycoproteinsprecipitating the glycoproteins contained in contained in saliva, tannins make the latter lose its lubricating saliva, tannins make the latter lose its lubricating power. power.

The combination between tannins and macromolecules The combination between tannins and macromolecules is established by hydrophobic interactions and hydrogen is established by hydrophobic interactions and hydrogen bonds between the bonds between the phenolicphenolic groups of tannins and the groups of tannins and the proteins or other polymers. proteins or other polymers.

Other types of linkages (irreversible) must also be Other types of linkages (irreversible) must also be involved to ensure the lasting stability of the combination involved to ensure the lasting stability of the combination between tannins and collagen structures. between tannins and collagen structures.

These include the covalent bonds established after These include the covalent bonds established after oxidation of the phenols to oxidation of the phenols to quinonesquinones. .

The condition necessary for the formation of these The condition necessary for the formation of these linkages is the tannin’s molecular weight must fall within linkages is the tannin’s molecular weight must fall within a well defined range. If it is too high, the molecule a well defined range. If it is too high, the molecule cannot insert itself into the cannot insert itself into the interfibrillarinterfibrillar spaces of the spaces of the macromolecule. If it is too low, the molecule can insert macromolecule. If it is too low, the molecule can insert itself but cannot form enough bonds to stabilize the itself but cannot form enough bonds to stabilize the combination.combination.

Tannins Tannins -- DefinitionDefinition

“Water“Water--soluble soluble phenolicsphenolics of molecular of molecular weight between 500 and 3 000, which, in weight between 500 and 3 000, which, in addition to displaying the classic reactions addition to displaying the classic reactions of phenols, can precipitate alkaloids, of phenols, can precipitate alkaloids, gelatine, and other proteins.”gelatine, and other proteins.”

A more recent definition of tannins: A more recent definition of tannins: ““Phenolic natural products that precipitate Phenolic natural products that precipitate proteins from their aqueous solutions”.proteins from their aqueous solutions”.

True Tannins Vs PseudoTrue Tannins Vs Pseudo--TanninsTannins

True tannins:True tannins: Molecular Molecular weights of 1000weights of 1000--5000.5000.

PseudoPseudo--tannins:tannins: Gallic Gallic acid, catechins and acid, catechins and chlorogenic acid are chlorogenic acid are similar phenolic similar phenolic compounds: have a compounds: have a low molecular weight.low molecular weight.

Tannin FunctionTannin Function

Tannins are of wide Tannins are of wide occurrence in plants occurrence in plants and are usually found and are usually found in in greatest quantitygreatest quantity in in dead or dying cellsdead or dying cells. . They They exert an exert an inhibitory effect on inhibitory effect on many enzymes due to many enzymes due to protein precipitationprotein precipitationand, hence, may and, hence, may contribute a contribute a protective protective functionfunction in barks and in barks and heartwoods. heartwoods.

Tannin IncompatibilitiesTannin Incompatibilities

Clove and cinnamon contain tannins and Clove and cinnamon contain tannins and also other principal therapeutic also other principal therapeutic constituents. constituents.

This may complicate extraction or produce This may complicate extraction or produce imcompatibilities with other drugs.imcompatibilities with other drugs.

E.g. Many alkaloids for example are E.g. Many alkaloids for example are precipitated by tannins.precipitated by tannins.

Tannin ExtractionTannin Extraction

Tannins are extracted using Tannins are extracted using waterwater and and acetoneacetone..

Optimal yields are obtained from Optimal yields are obtained from freshfreshtissues or freezetissues or freeze--dried tissues.dried tissues.

Optimal yields are not obtained from dried Optimal yields are not obtained from dried tissues (tannins are irreversibly combined tissues (tannins are irreversibly combined with other polymers)with other polymers)

After eliminating the acetone (distillation), After eliminating the acetone (distillation), the pigments and lipids are removed from the pigments and lipids are removed from the aqueous solution by a solvent the aqueous solution by a solvent extraction.extraction.

Ethyl acetateEthyl acetate extraction of the aqueous extraction of the aqueous solution separates the solution separates the dimericdimericproanthrocyanidinsproanthrocyanidins and most and most gallotanninsgallotannins..

Polymeric Polymeric proanthrocyanidinsproanthrocyanidins and and high high molecular weight molecular weight gallotanninsgallotannins remain in remain in the aqueous phase.the aqueous phase.

To obtain pure To obtain pure compounds, the compounds, the appropriate appropriate chromatographic chromatographic techniques are used techniques are used (most often one of the (most often one of the gel filtrations)gel filtrations)

Followed by reverseFollowed by reverse--phase phase chromatography (in chromatography (in water and alcohol, or water and alcohol, or water, alcohol and water, alcohol and acetone mixures)acetone mixures)

Medicinal Properties of TanninsMedicinal Properties of Tannins

Therapeutic/medicinal activities result due Therapeutic/medicinal activities result due to the to the astringencyastringency properties.properties.

Tannin containing herbs (drugs) will Tannin containing herbs (drugs) will precipitate proteins.precipitate proteins.

Externally: waterproof the external layers Externally: waterproof the external layers of the skin and mucosa: of the skin and mucosa: ProtectProtectunderlying layers.underlying layers.

VasoconstrictorVasoconstrictor effects effects –– on small on small superficial vessels superficial vessels

Medicinal Properties of TanninsMedicinal Properties of Tannins

Limits fluid lossLimits fluid loss –– enhance tissue enhance tissue regeneration in superficial wounds and regeneration in superficial wounds and burnsburns

Internally: Internally: AntiAnti--diarrhoealdiarrhoeal AntiAnti--septicseptic effects (antieffects (anti--bacterial/antibacterial/anti--

fungal) fungal) used to Rx infectious used to Rx infectious diarrhoeas and dermatitis.diarrhoeas and dermatitis.

AntiAnti--oxidant Activity of Tanninsoxidant Activity of Tannins Hydrolysable tanninsHydrolysable tannins (more so than (more so than

condensed tannins) are condensed tannins) are freefree--radical radical scavengers.scavengers.

Inhibit Inhibit superoxide ionsuperoxide ion formation.formation. Some Some inhibit lipoxygenaseinhibit lipoxygenase They do not inhibit cycloThey do not inhibit cyclo--oxygenase.oxygenase.

AntiAnti--oxidant flavonols and oxidant flavonols and proanthrocyanidins from grape juice and proanthrocyanidins from grape juice and wine are widely considered to be the main wine are widely considered to be the main principles responsible for the preventative principles responsible for the preventative effect of CVD.effect of CVD.

Enzymatic Inhibition ActionEnzymatic Inhibition Action

Tannins may act as enzyme inhibitors.Tannins may act as enzyme inhibitors.

They block They block 55--lipoxygenaselipoxygenase inhibit inhibit angiotensin converting enzymeangiotensin converting enzyme hyaluronidasehyaluronidase activationactivation glucosyltransferasesglucosyltransferases (of microorganisms (of microorganisms

involved in cavity formation).involved in cavity formation).

New (Hydrolysable) Tannin New (Hydrolysable) Tannin PotentialPotential

Tannins, including gallo and ellagic Tannins, including gallo and ellagic acid (epigallitannins), are inhibitors acid (epigallitannins), are inhibitors of HIV replication.of HIV replication.

1,3,41,3,4--TriTri--OO--galloylquinic acid galloylquinic acid 3,53,5--didi--OO--galloylgalloyl--shikimic acid, shikimic acid, 3,4,53,4,5--tritri--OO--galloylshikimic acid galloylshikimic acid punicalin punicalin PunicalaginPunicalagin

inhibited HIV replication in infected inhibited HIV replication in infected H9 lymphocytes with little H9 lymphocytes with little cytotoxicity. cytotoxicity.

Two compounds, Two compounds, punicalinpunicalin and and punicacortein C,punicacortein C, inhibited purified inhibited purified HIV reverse Transcriptase.HIV reverse Transcriptase.

Classification of TanninsClassification of Tannins