Tannins and tannins drugs

Tannins(Definition, Properties, Classification, chemical tests)

1. Tannins
Catechu, Pterocarpus
By-Maninderjit Kaur
Rayat-Bahra Institute of Pharmacy, Hoshiarpur

2. TANNINS
Definition:
Tanninsarenaturallyoccurringcomplexorganiccompounds
possessingnitrogenfreepolyphenolsofhighmolecular
weight.
Tannin,alsocalledtannicacid,anyofagroupofpale-
yellowtolight-brownamorphoussubstancesintheformof
powder,flakes,oraspongymass,widelydistributedinplants
andusedchieflyintanningleather,dyeingfabric,makingink,
andinvariousmedicalapplications.
Theyformcolloidalsolutionwithwatergivingacidreactions.
Theyalsoprecipitateproteinsandalkaloids.
Theastringentinnatureoftanninsisduetothefactthatthey
canprecipitateproteinsandrenderthemresistantto
enzymaticattack.
Whenappliedonawoundorinjury,tanninsformaprotective
coatingsoastopreventexternalirritationandthuspromote

4. Thetannincompoundscanbedividedintotwomajorgroupson
thebasisofGoldbeater’sskintest.
Agroupoftanninsshowingthepositivetanningtestmaybe
regardedastruetannins
whereasthose,whicharepartlyretainedbythehidepowderandfail
togivethetest,arecalledaspseudotannins.
Mostofthetruetanninsarehighmolecularweightcompounds.
Thesecompoundsarecomplexpolyphenolicswhichareproduced
bypolymerizationofsimplepolyphenols
Theymayformcomplexglycosidesorremainsassuchwhichmay
beobservedbytheirtypicalhydrolyticreactionwiththemineral
acidsandenzymes.
Twomajorchemicalclassesoftanninsareusuallyrecognized
basedonthishydrolyticreactionandnatureofphenolicnuclei
involvedinthetanninsstructure.
Thefirstclassisreferredtoashydrolysabletannins,whereasthe
otherclassistermedascondensedtannins.

5. Hydrolysable tannins:
Thesetanninsarehydrolyzedbyacids,orenzymeandproduce
gallicacidorellagicacid.
Ondrydistillationcondensedtanninproducepyrogallol
Chemically,theseareestersofphenolicacidlikegallicacidand
ellagicacid.
Thetanninsderivedfromgallicacidareknownasgallitannins
andfromthatofellagicacidareknownasellagitannins.
Thegallicacidisfoundinrhubarb,cloveandellagicacidis
foundineucalyptusleaves,myrobalansandpomegranate
bark.
Thesetanninstreatedwithferricchloridetoproducedblueor
blackcolour.
Condensed tannins or Non-Hydrolysable or Phlobatannins:
Thesetanninsareresistanttohydrolysisandtheyderived
fromtheflavonols,catechinsandflavan-3,4-diols.
Ontreatmentwithacidsorenzymestheyarepolymerisedor
decomposedintophlobaphenes
Ondrydistillationcondensedtanninproducecatechol.
Thesetanninsarecalledascatecholtannins.
Thesetanninsarefoundincinchonabark,malefern,areca
seeds,tealeavesandwildcherrybark,baherafruits,Amla,etc.
Theyproducebrownish-greencolourwithferricchlorides.

6. Pseudo tannins:
They are phenoliccompounds of lower molecular weight and
do not show the goldbeater’s test.
They are found in catechu and nux-vomica, etc.
PROPERTIES OF TANNINS:
Tannins are freely soluble in water, alcohol, glycerol, and
acetone and dilute alkalis.
They are sparingly soluble in chloroform, ethyl acetate and other
organic solvents.
They have an astringent taste.
They yield purple, violet or black precipitate with iron
compounds.
They are precipitated by number of metallic salts notably
potassium dichromate, and lead acetate and sub acetate.
They combine with skin and hide to form leather and with gelatin
to form an insoluble compound. They combine with alkaloids
to form tannates, most of which are insoluble in water.

7. “Thecomplexorganicnonnitrogenous,poly
phenolicsubstancesofhighmolecularweight.”
Medicinal&BiologicalProperties
Tanninsarethedrugswhichcanstophemorrhage
Theyprecipitateproteins.
Theyareusedasanastringent.
Theyareusedinthetreatmentofburns.
Theyactasantidiarrheal.
Theyareemployedasanantidoteforheavy
metalpoisoning.
Theyaremostpotentantioxidant.

8. CHEMICAL TESTS
Gelatintest:
Toasolutionoftannin,aqueoussolutionofgelatinand
sodiumchlorideareadded.Awhitebuffcolouredprecipitate
isformed.
Goldbeater’sskintest(Importanttestoftannins)
Asmallpieceofgoldbeaterskin(membranepreparedfrom
theintestineofanox)issoakedin20%hydrochloricacid,
rinsedwithdistilledwaterandplacedinasolutionoftanninfor
5minutes.
Theskinpieceiswashedwithdistilledwaterandkeptina
solutionofferroussulphate.Abrownorblackcolouris
producedontheskinduepresenceoftannins.
Phenazonetest:
Amixtureofaqueousextractofadrugandsodiumacid
phosphateisheatedandcooledandfiltered.Asolutionof
phenazoneisaddedtothefiltrate.
Abulkycoloredprecipitateisformed.

9. Matchsticktest(Catechintest):
Amatchstickisdippedinaqueousplantextract,
driednearburnerandmoistenedwith
concentratedhydrochloricacid.
Onwarmingnearflame,thematchstickwood
turnspinkorredduetoformationofphloroglucinol
Chlorogenicacidtest:
Anextractofchlorogenicacidcontainingdrugis
treatedwithaqueousammonia.
Agreencolourisformedonexposuretoair.

11. Catechu
Synonyms–Pale catechu, gambier, catechu
Biological source –It consists of the dried aqueous extract prepared from
the leaves of Uncaria gambier
Family-Rubiaceae
Chemical constituents –
Palecatechucontainfromabout7to30%ofpseudotannincatechin
and22to55%ofaphlobatannincatechutannicacid
Itcontainsflavonoidslikequercetinandfluorescentsubstances
Gambierfluorescein.
Italsocontainscatechu-red,pyrogallol,fixedoilandwaxes
Catechinformswhite,needlelikecrystals,whichdissolvesinalcohol
andhotwater.Catechutannicacidgivesgreencolourwithferricchloride.
Uses –
Used as an astringent
Used in the treatment of diarrhoea
Large proportion of gambier is used in dyeing and tanning industries

12. BLACK CATECHU
Synonym:Cutch, black catechu, kattha
Biological source –It consists of the dried aqueous extract prepared
from heart wood of Acacia catechu
Family -Leguminosae
Chemical constituents –It contains about 2–12% of catechinand
about 25 to 33% of phlobatannincatechutannicacid.
Theprinciplefractionofcutchhasbeenidentifiedasamixtureof
catechinisomerswhichincludes(-)epicatechin,acacatechin,DL-
acacatechin,L-acacatechinandD-isoacacatechin
It contains flavonoidslike quercetin.
Others like Catechu-red and gum
Uses –Used as an astringent
It cures troubles of mouth, diseases of the throat and diarrhoea.
In India and eastern countries, it is used in betel leaves for chewing
Marketed Products
It is one of the ingredients of the preparation known as Kofletlozenge
(Himalaya Drug Company) as cough expectorant, and Gum tone
(CharakPharmaPvt. Ltd.).

13. CHEMICAL TESTS FOR CATECHU
1.GambirFluorescintest-Alcoholicextractofdrug,fewdrops
ofsodiumhydroxide
Mixandaddpetroleumether,shakeandkeptasideforfew
minutes–petroleumetherlayershowsgreenfluorescence(
+veforpalecatechudueGambirFluorescin)
2.Matchsticktest(Catechintest)–Amatchstickisdippedin
aqueousplantextract,driednearburnerandmoistenedwith
Hcl
Onwarmingnearflame,thematchstickwoodturnspinkor
redduetotheformationofphloroglucinol
3.Vanillin–Hydrochloricacidtest–Testsolutionandfew
dropsofVanillin–Hydrochloricacidreagent–Aredorpinkis
formedduetheformationofphloroglucinol
4.Chlorophylltest-Powdereddrugisheatedwithchloroform
onawaterbathfor1-2minutes.Theorganiclayerisfiltered
inachinadishandevaporatedonthewaterbath–green
residue

14. Pterocarpus
Synonyms-bijasal, Indian kino tree, Malbar kino
Biological source-it can consist dried juice obtained by
making vertical incisions to the stem bark of the
plantPterocarpus marsupium belonging to family
leguminosace.
Geographical source-Gujrat, Madhya pradesh, uttar
pradesh, bihar
Chemical constituents-
70% to 80% kinotannic acid , kino red , k-pyrocatechin
Kinotannic acid is glucosidal tannin, whereas kino-red is
anhydride of kinoin. Kinoin is an insoluble phlobaphene
Chemical test-drug treated with ferrous sulphate shows
green colour. Drug + alkali shows violet colour. Mineral
acid shows ppt.
Use-–it is used as astringent of diarrhoea and local
astringent in the form of lozenges. dyspepsia , purgative.