Pharmacognosy II (BPM-225),

 

 Distribution, properties, tests, extraction, structure types and classification.  

The details of the following: 

1. Pyridine-piperidine: Areca  

2. Tropane: Belladonna, stramonium, Hyoscyamus and Coca  

3. Quinoline: Cinchona  

4. Isoquinoline:Opium  

5. Indole: Rauwolfia, Ergot  

6. Steroidal: Veretrum viride, aconite  

7. Purine bases: Coffee, Tea  

 

 

•Pharmacognosy is the study of plants or other natural sources as a possible source of drugs.  

•The American Society of Pharmacognosy defines pharmacognosy as "the study of the physical, chemical, biochemical, and biological properties of drugs, drug substances, or potential drugs or drug substances of natural origin as well as the search for new drugs from natural sources"  

Background Medicinal Plants 

 Plants that enable therapeutic properties or favorable pharmacological effects on human body are generally designated as medicinal plants. The commonly occurring chemical substances which are responsible for the medicinal (as well as toxic) properties of plants, include the following:  

 

Gums and Mucilage: Chemically these are complex carbohydrates containing monosaccharide units (pentose and hexose). The also contain uronic acid, sulphate ions and Ca and Mg salts.  

 

Fixed Oils: Chemically esters of fatty acids and glycerol. The common fatty acids that occur in fixed oils are: Capric, lauric, myristic, palmitic, stearic, arachidic, oleic, linoleic and ricinoleic acids.  

 

Volatile or Essential Oils: Chemically volatile oils are complex mixture of hydrocarbons and their oxygenated derivatives, alcohols, ketones, aldehydes, ethers, oxides, esters etc.  

 

Background Ref.: Medicinal Plants of Bangladesh (2nd edition)-Abdul Ghani  

 

•Phenol: Such as salicylic acid and thymol  

•Tannins: Chemically, tannins are complex polyhydroxyphenolic substance.  

•Resins: Resins are amorphous complex chemical substances, which are mixture of resin acids, resin alcohols, resinotannols and esters.  

•Glycosides: Anthraquinone glycosides, cardiac glycosides, saponin glycosides, thiocyanate glycosides, miscellaneous glycosides.  

•Flavones and Flavonoids  

•Anthocyanins  

•Coumarins  

•Alkaloids and Amines: Pyridine group, Tropane group, Isoquinoline group, Quinoline group, Quinolizidine group, Indole group, Steroidal group, Imidazole group, Phenylethylamine group, Alkaloidal amines.  

•Vitamins and Minerals  

 

Definition: Alkaloids are basic, nitrogen containing compounds of plant origin. They have complex molecular structure with the nitrogen atom involved in a heterocyclic ring and they manifest a significant pharmacological activity.  

 

Some well-known alkaloids include :  

•morphine,  

•strychnine,  

•quinine,  

•ephedrine, and  

•nicotine.  

 

Chapter 2: Alkaloids  

Many alkaloids have potent physiological effects and therefore, are considered as important therapeutic agents e.g. atropine, morphine, quinine, reserpine etc.  

Alkaloids are widely used to treat diseases ranging from malaria to cancer.  

Some Alkaloids are extremely poisonous:  

•Ergot alkaloids are poisonous  

•The extracts of plants containing alkaloids have long been used as arrow poisons in hunting and warfare e.g. curare extract contains tubocurarine alkaloid.  

•At the time of the Roman Empire, Belladonna (the source of atropine) had been mixed with food with the purpose of murdering.  

• Cleopatra, the queen of Egypt used Egyptian henbane (Hyoscyamus muticus) that contains hyoscyamine, for suicidal purpose.  

Certain alkaloids are widely used for their psychotropic effects e.g. Caffeine acts as CNS stimulant  

 

Distribution & Occurrence of Alkaloids  

 

•Alkaloids are not equally distributed in plant kingdom.  

•It is nearly absent in Algae and lower plants (with some exceptions of Fungi) Fungal examples: Ergot and some Mushrooms  

•Strptomyces sp. Produce antibiotic alkaloids  

Chloromycetin (Chloramphenicol)  

Erythromycin  

 

•Alkaloids are mostly found in higher plants (Dicotyledonous plants e.g., most common garden plants, shrubs and trees, and broad-leafed flowering plants)  

 

•Alkaloids may present in the following parts of plant: 

 

 Whole plant  

•Datura  

In Barks:  

•Cinchona  

In Roots:  

•Rauwolfia, Belladonna, Aconite  

In fruits:  

•Black pepper  

In Leaves:  

•Hyoscyamus, Datura 

 In Seeds:  

•Nux-vomica, Areca  

 

Pharmaceutical and medicinal use of alkaloids  

Alkaloids show quite diverse medicinal properties. Some are as following:  

Morphine:  

•Morphine is one of the most known alkaloids which had been used and still is for medical purposes.  

•This alkaloid is a powerful narcotic which is used for the relief of pain, but its usefulness is limited because of addictive properties  

 

Fig. Structure of Morphine  

 

Atropine:  

•Atropine is the alkaloid which is used as medication in many clinical applications .  

•For example, injection with atropine is given to treat bradycardia (low heart rate).  

 

Fig. Structure of Atropine  

 

Tubocurarine:  

• an alkaloid,  

•used in surgery as muscle relaxant.  

 

            Fig.: Structure of tubocurarine.  

 

Pharmaceutical and medicinal use of alkaloids  

vincristine and vinblastine  

•Alkaloids vincristine and vinblastine are used as chemotherapeutic agent in the treatment of many cancer types.  

 

Cocaine: Cocaine is an alkaloid present in Erythroxylum coca, is a potent local anesthetic.  

Ergonovine & Ephedrine  

•Ergonovine, an alkaloid from the fungus Claviceps purpurea, and the second alkaloid ephedrine isolated from Ephedra species both act as blood vessel constrictors.  

•Ephedrine is also used in bronchial asthma and to relieve discomfort of hay fever, sinusitis, and common colds.  

Quinine  

•Quinine is a powerful antimalarial agent and more often is replaced by synthetic drugs, which are more effective and less toxic.  

 

 

Fig. Structure of quinine from Cinchona species. 

Quinidine:  

•Another alkaloid from Cinchona species is quinidine which has medical application as treatment of irregular rhythms of the heartbeat or arrhythmias.  

 

Colchicine  

•Colchicine is another alkaloid, present in plants of Liliaceae family, known for ages to treat acute gout attacks.  

 

 

       Fig. Structure of colchicine 

 

 

Chemical Test for Detection of Alkaloids  

Dragendorff’s test:  

•Reagent Preparation: Bismuth Nitrate 8.00 g, Nitric Acid 20.5 g, Potassium Iodide 27.2 g Water qs 100.0 mL                                                                                   •To 2 mL of the extract, add 1 mL of Dragendorff’s reagent along the side of the test tube. Formation of orange or orange reddish brown precipitate indicates the presence of alkaloids. 

 Mayer’s reagent test •Mayer's reagent is a solution of potassium mercury iodide in water. [Dissolve mercuric chloride (2.72 g) in distilled water (120 ml). Separately dissolve potassium iodide (10 g) in distilled water (40 mI). Mix the two solutions and make up to volume (200 ml) with distilled water.)] 

•A general presumptive test for cocaine, morphine, heroin, and other alkaloids  

•A positive result is indicated by a cream precipitate.  

 

 

Hager’s reagent test:  

•Picric acid  

•Gives yellow crystalline precipitation with alkaloids.  

 

Chemical Test for Detection of Alkaloids  

 

Tannic Acid Solution(%5 w/v)  

•It gives buff colored (light brownish yellow) precipitation which is soluble in diluted acid or ammonia.  

Ammonium Reineckate Solution (2% v/v)  

•The solution produces yellow-orange precipitates with heterocyclic nithrogen alkaloids, with quaternary and some tertiary amines.  

 

Wagner’s reagent test:  

•Reagent Preparation: Iodine 1.3 g, Potassium Iodide 2.00 g & Water qs 100.0 ml   

 

Other Methods of Detection of Alkaloids  

 

Chromatographic Analysis  

 

•Thin-Layer Chromatography (TLC)  

•Gas Chromatography (GC)  

•Liquid Chromatography (HPLC)  

•Capillary Electrophoresis  

•Countercurrent Chromatography  

 

Spectrometric Techniques  

 

•Nuclear Magnetic Resonance (NMR) Spectrometry  

•Mass Spectrometry (MS)  

Alkaloids; R Verpoorte, Gorlaeus Laboratories, Leiden, The Netherlands; 2005  

Properties of Alkaloids  

 

Physical Properties:  

 

Alkaloids are usually odorless, colorless, crystalline, non-volatile, bitter solids.  

Few are colored eg. Berberine and colchicine are yellow or show strong fluorescence (e.g., quinine).  

Some colorless alkaloids may have colored salts eg. Hydrastinine salt is yellow and Sanguinarine salt is red.  

In pure state, alkaloids and their salts are crytallizable solids.  

Few bases are oily liquids eg. Arecoline, Coniine, Nicotine, Pilocarpine and sparteine.  

Few alkaloids are amorphous eg. Emetine  

 

 

Free alkaloidal bases:  

•Usually soluble in organic solvents such as Chloroform, Ether or other non-polar immiscible solvents as well as lower Alcohols.  

•Practically insoluble or sparingly soluble in Water. Exceptions:  

•Few alkaloidal bases are sparingly soluble in organic solvents eg. Morphine in Ether (1:5000), Pilocarpine and Narceine are insoluble.  

•Few alkaloidal bases are soluble in Water eg. Caffeine, Ephedrine, Colchicine, Pilocarpine and quaternary alkaloidal bases like Tubocurarine and Berberine.  

Alkaloidal Salts:  

•Generally soluble in Water  

•Less soluble in Alcohols  

•Insoluble or sparingly soluble in Organic Solvents. Exceptions:  

•Quinine sulfate is sparingly soluble in Water (1:1000)  

•Few alkaloidal salts are soluble in organic solvents eg. Apoatropine hydrochloride and Lobaline hydrochloride is soluble in Chloroform.  

 

Solubility:  

For information: Table 1.1: Descriptive Terms of approximate Solubility as per IP 1996  

 

•Alkaloids usually contain one nitrogen atom, yet certain alkaloids may contain more than one and up to 5 nitrogen atoms in their molecule e.g. nicotine contains two nitrogen atoms and ergotamine has five N atoms. These nitrogen atom usually exists in a heterocyclic ring.  

•Nitrogen in alkaloids exists in the form of amine. It may be:  

A primary amino group e.g. nor-pseudoephedrine  

A secondary amino group e.g. ephedrine.  

A tertiary amino group e.g. nicotine and atropine.  

A quaternary ammonium ion e.g. tubocurarine.  

•Most alkaloids are optically active (laevorotatory, e.g., (-) hyoscyamine) and are more pharmacologically active in contrast to the corresponding racemic mixtures which are characterized by lower activity. (Racemic mixture is one that has equal amounts of left (levorotary)- and right-handed (dextrorotary) enantiomers of a chiral molecule.)  

•In general, alkaloids are less stable in solution than in the dry state.  

•Alkaloids are decomposed by heat, except caffeine  

•Alkaloids are often quite unstable, and N-oxidation in particular is quite common. Besides the effect of heat and light, their stability is influenced by solvents.  

 

Chemical Properties:  

Alkaloids are mainly categorized in 4 ways:- 1.) Biosynthetic classification :-Based on types of precursor used for alkaloid biosynthesis in plants. 2.) Pharmacological classification :-Based on pharmacological response or use. 3.) Taxonomical classification :-Based on their distribution in various plant. 4.) Chemical classification :-It is probably most satisfactory way to classify the alkaloids.  

 

Classification of Alkaloids Chemical Classification of Alkaloids:  

Here, the alkaloids are classified according to the nature of heterocyclic ring. 1.Heterocyclic Alkaloid (Typical alkaloid) : Containing N atom in the heterocyclic ring. a. Pyrrolidine – Ex: Hygrine b. Piperidine – Ex: coniine c. Pyridine-piperidine -Ex: Anabasine d. Quinoline – Ex:quinine, quinoline e. Isoquinoline – Ex:papavarine f.Indole –Ex: Lysergicacid g. Pyrrolidine –Pyridine – Ex: Nicotine h. Phenanthrene – Ex: Morphine i. Tropane –Ex: Atropine  

2. Non-heterocyclic Alkaloid (Atypical alkaloid): a. Phenylethyl amine (Amino alkaloid)–Ex: Ephedrine b. Tropolone –Ex: Colchicine  

 

 

 

 Extraction/Isolation of Alkaloids Procedures for isolation/extraction of alkaloids include the major following steps:  

 

preparation of the plant sample  

liberation and extraction of the free alkaloidal bases  

purification and fractionation of the crude extract  

isolation of individual alkaloids.  

 

Preparation of the plant sample : The collected plant material is carefully  

dried  

powdered  

defatted with petroleum ether (e.g. in case of seeds). (if necessary, ) (Note: Although most alkaloids are insoluble in petroleum ether, yet the extract should be tested before rejection.)  

 

 

Extraction & purification For extraction of alkaloids, one of the following methods are applied: Method I:  

1.The powder is treated with lime water, that liberates the free bases if present as salts, and combines with acids, tannins or other phenolics.  

2.The alkaline extract is then shaken with a suitable organic solvent, generally chloroform.  

3.The organic layer is separated and concentrated (containing free alkaloids and lipophilic impurities).  

4.The concentrated organic extract is then shaken with aqueous acid and allowed to separate.  

5.This separates alkaloids as their salts (in the aqueous layer) from most other impurities, which remain in the organic layer (purification).  

 

 

Extraction & purification Method II:  

1.The powdered material is extracted with water or aqueous alcohol containing dilute acid.  

2.Alkaloids are extracted as their salts together with accompanying soluble impurities.  

3.The acidic extract is shaken with chloroform or other suitable organic solvent to remove pigments and other undesirable impurities (weak bases may be present).  

 

 

Liberation and extraction of alkaloidal bases:  

The acid extracts (alkaloidal salts) resulting from either methods I or II are treated with dilute alkali  

•Generally sodium bicarbonate or ammonia is used to liberate the free bases  

These free bases are separated by filtration or extraction with organic solvents.  

 

 

Separation of individual alkaloids Separation can be carried by:  

Fractional precipitation or crystallization:  

This is generally performed after derivatization to salts such as oxalates, tartrates and picrates.  

Gradient pH extraction:  

This method is suitable for separating alkaloids of different basicity (weakly, moderately and strongly basic).  

The crude mixture is dissolved in 2% tartaric acid and extracted with organic solvent.  

The pH of the aqueous solution is gradually increased to pH 9,  

after each increment in pH, it is extracted with organic solvent.  

Chromatographic techniques:  

These are the most suitable in case of complex mixtures.  

Extraction/Isolation of Alkaloids Hot water extraction Five kilograms of dried leaves is boiled in eight litres of water for two hours, and then drained and reboiled for the second time at 100 οC for 2 hours. The aqueous extract is blow dried to give 375 g of the extract. Methanolic and alkaloid extract Dry, powdered leaves were soaked in methanol for several days at room temperature. The mixture was filtered and methanol was removed by rotary evaporator to give the crude methanolic extract. Procedure of extraction and evaporation was repeated three times. As for preparation of crude alkaloid mixture, the methanol extract was mixed with acetic acid-water (9:1), 1 part methanol extract to 35 parts acetic acid. Alternatively acid extraction was done by triturating the methanol extract with 5% aq. HCl. The suspension was then filtered and the filtrate was washed with petroleum ether. The acidic layer was basified with sodium carbonate to pH 9 and extracted with chloroform several times. The combined chloroform extract was dried over sodium sulphate and evaporated to give the crude alkaloid mixture. Molecules 2009, 14(10), 3964-3974; https://doi.org/10.3390/molecules14103964 Mitragyna Speciosa (Rubiaceae Family) Leaves  

 

 

Pyridine-piperidine:  

 

Areca    

 

Botanical name:  

•Areca catechu. Areca is the Spanish and Portuguese term for betel nut and catechu is the East Indian name for astringent extract or juice. Family :  

•arecaceae. Synonym:  

•Betel nut, semen areca, areca.  

Part used:  

•Seeds  

Constituents: Areca contains many pyridine derivatives alkaloids, with a total alkaloid content of 0.45 %. These alkaloids include:  

Uses:  

•The seeds are cut into narrow pieces and rolled inside betel pepper leaf on which lime is rubbed over and chewed by natives. Known as pan supari and is used as a masticating agent.  

•Areca is also used as anthelminthic in veterinary practice for tapeworm.  

 

• Arecoline: Arecoline is a colourless oily liquid alkaloid and is up to 0.2 % of the total.  

•Arecolidine  

•Guacine  

•Guavacoline and  

•a number of other alkaloids Other constituents of areca seeds include: Tannins-up to 15 %, Lipids, volatile oils and gums.  

 

 

 

Tropane Alkaloids  

 

Belladona 

  

History • Used as: Medicine, cosmetic, and poison • Ancient Romans: poisons • Medicine: anesthetic – produces delirium and hallucinations • Cosmetics: juice of leaf and berry applied to eye to dilate the pupil, to looks beautiful Synonym:  

•Deadly night shade leaves  

•Death’s herb  

•Poison black cherry  

Biological source: • It consists of dried leaves and flowering tops of Atropa belladonna Linn. (Solanaceae). • It contains about 0.35% of total alkaloids calculated as hyoscyamine. 

 Distribution: USA, UK, Germany and some parts of India. 

 Chemical composition  

• Belladonna contains 0.3–1.0% total alkaloids  

• The prominent base is l-hyoscyamine and other components are atropine, apoatropine  

• Other chemical constituents are choline, belladonnine, cuscohygrine, homatropine, hyoscyamine  

• Volatile bases, such as atroscine, leucatropic acid 

 • Flavonoids like rutin, kaempferol-3-rhamnogalactoside and 7-glucoside, quercetin-7- glucoside 

  

Uses  

• The drug is used as adjunctive therapy in the treatment of peptic ulcer; functional digestive disorders, including spastic, mucous and ulcerative colitis; diarrhoea, diverticulitis and pancreatitis. 

 • Due to anticholinergic property, it is used to control excess motor activity of the gastrointestinal tract and spasm of the urinary tract.  

• Belladonna is anticholinergic, narcotic, sedative, diuretic, mydriatic and used as anodyne and to check secretion.  

• It relieves spasm of gut or respiratory tract.  

 

Stramonium  

Tropane Alkaloids  

 

•Synonym: Stramonium leaves, Thorn Apple leaves, Jimson, Jamestown weed  

 

•Botanical Name: Datura stramonium  

 

•Geographical Source/Distribution: Datura stramonium grows wild in most tropical countries including: Nigeria, Bangladesh, India and south America, and cultivated in Spain, France, Germany, England and Hungary.  

 

•Botanical source: The drug consists of much shriveled and twisted mass of leaves, flowers, young fruits and slender stems.  

 

•Chemical composition  

It contains 0.2-0.45% oftropane alkaloids, principal one being hyoscyamine and hyoscine  

Other tropane alkaloids like atropine, littorine, tigloidine, meteloidine, tropine, pseudotropine are also present in smaller quantity.  

 

•Uses  

Stramonium is a parasympatholytic and decrease the flow of secretion of saliva, milk and sweat  

Also used as mydriatic agent, sedative and anodyne.  

 

Coca  

Tropane Alkaloids  

 

•Synonym: Coca leaves, Folia cocae  

 

•Geographical Source/Distribution:  

Coca plants are cultivated in Peru, Bolivia, Java and Formosa  

No wild variety is known  

 

•Botanical source:  

it consist of dried leaves of Erythroxylon coca and E. truxillense (erythroxylaceae)  

Erythroxylon coca - Bolvian coca  

E. truxillense – Peruvian/ truxillo coca  

 

 

•Chemical composition  

•Coca leaves contain 0.5-1.5% of tropane alkaloids, most important of which is cocaine.  

•Other tropane alkaloids include: truxilline, ecgonine, and benzoylecgonine  

•Peruvian and Java coca leaves are richer in total alkaloid content  

•In addition to the tropane alkaloids, they contain cocatannic acid.  

 

•Uses • As local anaesthetic in minor surgical operations • Used as lead molecule to develop new LA (Local Anesthetics) • In general, it is used as stimulant, restorative and convulsion  

•An addictive alkaloid and is a drug of abuse.  

 

 

Hyocyamus  

Tropane Alkaloids  

 

•Synonym: Common Henbane, Hyoscyamus, Hog’s-bean, Jupiter’s bean,  

 

•Botanical Name: Hyoscyamus niger Linn  

 

•Geographical Source/Distribution:  

•Central and Southern Europe; Western Asia, extending to India  

 

•Biological source:  

•consists of the dried leaves and flowering tops of Hyoscyamus niger Linn., belonging to family Solanaceae.  

 

 

•Uses:  

The leaves have long been employed as narcotic medicine.  

It is used as antispasmodic, hypnotic and mild diuretic  

It has tranquilizing effect in person with severe nervous irritability, producing a tendency to sleep.  

Combined with silver nitrate, it is especially useful in the treatment of gastric ulcer and chronic gastric catarrh ( excessive discharge of mucus in nose and throat)  

 

•Chemical composition:  

Major constituents are tropane alkaloid- 0.045% - 0.14% including hyoscyamine together with smaller quantity of atropine and hyoscine  

Other constituents: Hyoscytricin  

It also contains choline, mucilage, calcium oxalate, and potassium nitrate.