Resins and resin combination ; Tannins

Lecture ( 7 ) Pharmacognosy ( II )

Resins and resin combination ; Tannins
Resins : are amorphous products with a complex chemical nature , they are end products of metabolism , usually formed in ducts or cavities in plant tissues .
Physically , Resins are usually hard , transparent , or translucent , when heated , they are complex mixtures of resin acids , resin alcohols , resinotannols , esters and resenes . They are insoluble in water .
Several resins are used in Pharmacy and in the Arts , among which rosin , guaiac , and mastic are typical examples .
Resins often occur in more or less homogeneous mixtures with Volatile Oils ; the mixtures are known as ( Oleoresins ) as Turpentine and Ginger
Oleoresins also occur in mixtures with gums , these mixtures called Oleo – gum – resins include Myrrh , from ( Commiphora sp. ) .
Balsams : are resinous mixtures which contain Cinnamic acid , Benzoic acid , or both , or esters of these acids . ( Benzoin , Peru balsam , Tolu balsam and Storax ) are typical balsams.
Resins properties : when resins are separated and purified they are usually :

1- Brittle , amorphous solids , fuse if heated .
2- Insoluble in water , but dissolve in alcohol or other organic solvents .
3- On evaporation these solutions deposit the resin as a varnish like film .
4- Resin burn with a characteristic , smoky flame .
Resins may be the final products in destructive metabolism

Principal Constituents of Resins may be Classified as Follows

Resin acids : Contain a large proportion of diterpenoid oxyacids , usually Combining the properties of Carboxylic acids and phenols . They occurs in free states and esters. They are soluble in aqueous solutions of the alkalies , usually forming soap like solutions or colloidal suspensions . Their metallic salts are known as resinates and some of these resinates are used in the manufacture of cheap soaps and varnishes . Ex . of Resin acids are ( abietic acid in rosin or Colophony and Commiphoric acid in Myrrh ) .

Resino tannols : are complex alcohols of high molecular weight , it gives a tannin reaction with iron salts . Ex. of resinotannols : (Peruresinotannol from Balsam of Peru , Siarresinotannol and Sumaresinotannol from benzoin and Toluresinotannol from Balsam of Tolu ) .
Ex. of resinols are : Benzoresinol from benzoin and Storesinol from Storax .

Pharmaceutic resins are usually obtained :
1- By extracting the drug with alcohol and precipitating the resin in water .
2- By separating the oil from oleoresin by distillation , as with rosin from turpentine .
3- By collecting the natural product that has exuded as oleoresin from the plant through natural or artificial punctures and from which the natural oil has partially evaporated in to the atmosphere , as with mastic .

Rosin :
Rosin or Colophony is a solid resin obtained from ( Pinus palustris Miller ) and other species of Pinus .
Rosin has a great variety of technical uses . Only the light – colored transparent rosins are used medicinally .

Rosin is used as a stiffening agent in Cerates , Plasters , and Ointments .
Eriodictyon :
Eriodictyon : is the dried leaf of ( Eriodicyton californicum ) , Eriodictyon contains a resin , eriodictyol ( the aglycone of eriodictin) .

Eriodictyon is a flavor used to disguise the bitterness of certain preparations such as those containing Quinon .It has also been used as a Stimulating expectorant .

Mastic : is the concrete resinous exudate from ( Pistacia lentiscus L. ) , mastic contains about 90% of a resin .

Kava : is the dried rhizome and roots of ( Piper methysticum Forster ) , it contains about 5 – 10 % of resin , Pharmacologic studies have shown that all of the Kava pyrones , centrally acting skeleton muscle relaxants , also they possess antipyretic and local anesthetic properties .

Cannabis : consists of the dried flowering tops of the plant ( Cannabis sativa L. ) , its resin known as ( Hashish ) .
Either the resin ( Hashish ) or the flowering tops of the female plant ( Marihuana ) is used drug purposes .
By smoking Marihuana , the drug effects are noticeable almost immediately , users experience euphoria and relaxation . Thought processes are slowed , short - term memory impaired , and one has difficulty concentrating .

Tannins : Comprise a large group of complex substances that are widely distributed in the plant Kingdom . They are usually localized in specific plant parts , such as ( Leaves , Fruits , Barks , or Stems ) .
Tannins usually occur as mixtures of Polyphenols that are difficult to separate because they do not crystallize .
Tannins form with water a colloidal solutions .
Tannins cause precipitation of solutions of gelatin , and they precipitate proteins . When tannins applied to living tissue this action is known ( Astringent ) .
Tannins- bearing drugs , such as Hamamelis and Nutgall , Tannic acid and their derivatives are used in medicine as ( astringents ) in the gastrointestinal tract and on skin abrasions . In the treatment of burns , the proteins of the exposed tissues are precipitate and form a mildly antiseptic , protective coat under which the regeneration of new tissues may take place .
The principal constituent of Galls is 50 – 70 % ( Tannic acid ) , and 2 – 4 % ( Gallic acid ) , Ellagic acid , Starch and Resin .

Tannic acid ; Gallotannic acid , or Tannin : is a tannin usually obtained from nutgall .
Tannic acid : is a mixture of esters of gallic acid with glucose , Tannic acid is astringent , it was formerly used in the treatment of burns , but this application has been discontinued . Its topical use is now restricted to the treatment of bed sores , minor ulcerations , as an alkaloidal precipitant , it has been employed in cases of alkaloidal poisoning .

Gallic acid :
Bismuth subgallate is used by ostomates to help control odors.

Professor Dr. Saad Ali Ihsan
Ph.D. in Pharmacognosy & Medicinal Plants