Alkaloids: Introduction, Property and classification
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The document provides a comprehensive overview of alkaloids, including their definitions, classifications, physical and chemical properties, and methods of extraction and identification. It distinguishes between primary and secondary metabolites and discusses the specific characteristics of alkaloids, such as their nitrogen content and solubility. Additionally, it details various chemical tests used to detect alkaloids and their biosynthetic classifications based on precursor amino acids.
Alkaloids: Introduction, Property and classification
- 1. ALKALOID: AN OVERVIEW Presented by Mr. O. P. Verma Associate Professor Dept. of Pharmacognosy Goel Institute of Pharmacy and Sciences, Lucknow
- 2. Content ➢Metabolites ➢Definition ➢Exceptions with respect to definition ➢Distribution, occurence & forms of alkaloids. ➢Physical & chemical properties ➢Classification of alkaloids ➢Chemical test for alkaloids ➢Extraction, isolation & purification of alkaloids
- 3. Primary Metabolites Secondary Metabolites The metabolites which are required for the growth and maintenance of cellular function are called primary metabolites Secondary metabolites do not play a role in growth, development, or reproduction. However, they play a role in ecological functions like defense mechanisms, serve as antibiotics, and produce pigments. Primary metabolites are compounds that are directly involved in the growth and development of a plant They also indirectly support the cell, in sustaining their life for long duration. Produced in large quantity and extraction is easy Produced in small quantity and extraction is difficult Primary metabolites are a part of the basic molecular structure of an organism. Secondary metabolites are not a part of the basic molecular structure of an organism. Ex. vitamins, amino acids, nucleosides and organic acids Ex. alkaloids, Glycosides, steroids, antibiotics, toxins Difference between Primary Metabolites and Secondary Metabolites
- 4. Alkaloids Definition Alkaloids are basic heterocyclic nitrogenous compounds of plant origin that are physiologically active.
- 5. Modified Definition: Alkaloids are cyclic organic compounds containing nitrogen in a negative state of oxidation with limited distribution among living organisms.
- 6. Exceptions with respect to definition: ➢Basicity: Some alkaloids are not basic e.g. Colchicine, Piperine, Quaternary alkaloids. ➢Nitrogen: The nitrogen in some alkaloids is not in a heterocyclic ring e.g. Ephedrine, Colchicine, Mescaline. ➢Plant Origin: Some alkaloids are derived from Bacteria, Fungi, Insects, Frogs, Animals.
- 7. Distribution and occurence: Rare in lower plants. Families rich in Alkaloids: Apocynaceae, Rubiaceae, Solanaceae and Papaveracea. Families free from Alkaloids: Rosaceae, Labiatae.
- 8. Distribution in Plant: ➢All Parts e.g. Datura. ➢Barks e.g. Cinchona ➢Seeds e.g. Nux vomica ➢Roots e.g. Aconite ➢Fruits e.g. Black pepper ➢Leaves e.g. Tobacco ➢Latex e.g. Opium
- 9. Forms of Alkaloids: ➢Free bases ➢Salts with Organic acids e.g. Oxalic, acetic acids ➢Salts with inorganic acids e.g. HCl, H2SO4. ➢Salts with special acids: e.g. Meconic acid in Opium Quinic acid in Cinchona ➢Glycosidal form e.g. Solanine in Solanum.
- 10. Function in Plants ➢Protective. ➢Detoxification. ➢Source of nitrogen. ➢Growth regulators. ➢Source of energy.
- 11. Physical Properties: I- State: ➢ Most alkaloids are crystalline solids. ➢ Few alkaloids are amorphous solids e.g. emetine. ➢ Some are liquids that are either: Volatile e.g. nicotine and coniine, or Non-volatile e.g. pilocarpine and hyoscine. II- Colour: The majority of alkaloids are colorless but some are colored e.g.: ➢ Colchicine and berberine are yellow. ➢ Canadine is orange. ➢ Betanedine is red.
- 12. III- Solubility: ➢ Both alkaloidal bases and their salts are soluble in alcohol. ➢ Generally, the bases are soluble in organic solvents and insoluble in water Exceptions: ➢ Bases soluble in water: caffeine, ephedrine, codeine, colchicine, pilocarpine and quaternary ammonium bases. ➢ Bases insoluble or sparingly soluble in certain organic solvents: morphine in ether, theobromine and theophylline in benzene. ➢ Salts are usually soluble in water and, insoluble or sparingly soluble in organic solvents. Exceptions: ➢ Salts insoluble in water: quinine monosulphate. ➢ Salts soluble in organic solvents: lobeline and apoatropine hydrochlorides are soluble in chloroform.
- 13. Chemical Properties: I- Nitrogen: Primary amines R-NH2 e.g. Norephedrine Secondary amines R2-NH e.g. Ephedrine Tertiary amines R3-N e.g. Atropine Quaternary ammonium salts R4-N e.g d-Tubocurarine II- Basicity: ➢R2-NH > R-NH2 > R3-N ➢ Saturated hexacyclic amines are more basic than aromatic amines.
- 14. III- Oxygen: ➢Most alkaloids contain Oxygen and are solid in nature e.g. Atropine. ➢Some alkaloids are free from Oxygen and are mostly liquids e.g. Nicotine.
- 15. IV- Stability: ➢Effect of heat: Alkaloids are decomposed by heat, except Strychnine and caffeine (sublimable). ➢Reaction with acids: 1- Salt formation. 2- Dil acids hydrolyze Ester Alkaloids e.g. Atropine
- 16. General Classification: ➢True (Typical) Alkaloids that are derived from amino acids and have nitrogen in a heterocyclic ring. e.g Atropine ➢Protoalkaloids that are derived from amino acids and do not have nitrogen in a heterocyclic ring. e.g Ephedrine ➢Pseudo alkaloids that are not derived from amino acids but have nitrogen in a heterocyclic ring. e.g Caffeine ➢False alkaloids are non alkaloids give false positive reaction with alkaloidal reagents.
- 18. Chemical classification: 1. Pyrrolidine derivatives Ex. Hygrine, cocaine etc. 2. Pyperidine derivatives Ex. Piperine, lobeline etc.
- 19. 3. Pyrrolizidine derivatives Ex. Echimidine, Symphatine etc. 4. Tropane derivatives Ex. Atropin
- 20. 5. Quinoline derivatives Ex. Quinine, cinchonin, Cinchonidine etc. 6. Isoquinoline derivatives Ex. Morphine, narcotine, Narcein, codein etc.
- 21. 7. Indole derivatives Ex. Vincrisrine, Vinblastine, etc. 8.Imidazole derivatives Ex. Pilocarpine, Isopilocarpine etc.
- 22. 9. Aporphine derivatives. Ex. Boldine etc. 10. Quinazoline derivatives. Ex. Vasaka etc.
- 23. 11. Purine derivatives Ex. Caffeine etc. 12. Diterpene derivatives. Ex. Aconotine.
- 24. 13. Steroidal alkaloids. Ex. Solanidine 14. Duazocin alakloids Ex. Lupanine.
- 25. Biosynthetic classification: Alkaloids Precursor Example Indole alkaloids Trymptophan amino acid. vincristine, vinblastin etc. Piperidine alkaloids lysine amino acid (piperin, lobaline etc. Pyrrolidine alkaloids ornithine amino acid. Nicotine etc. Isoquinoline alkaloids tyrosine. morphine, codein, emetine etc. Imidazole alkaloids histidine pilocarpine, isopilocarpine etc. Amino/proto alkaloids phenylalanine amino acid. ephedrine etc. Quinazolidine alkaloids Lupinine amino acid. vasaka etc.
- 26. Chemical tests for alkaloids : 1. Dragendorff’s test- Dragendorff’s reagent (Potassium-bismuth-iodide solution) Test- 1ml of drug+1ml of dragendorff’s reagent- A reddish brown ppt. shows presence of alkaloids
- 27. 2. Mayer’s test- Mayer’s reagent (Potassium mercuric iodide solution) Test- 1ml of drug extract+1ml of mayer’s reagent- Whitish or cream coloured ppt shows presence of alkaloids.
- 28. 3. Hager’s test- Hager’s reagent (Saturated aq. solution of picric acid) Test- 1ml of drug extract+3ml of hager’s reagent Yellow coloured ppt shows presence of alkaloids.
- 29. 4. Wagner’s test- Wagner’s reagent (Iodine-potassium-iodide solution) Test- Drug extract+wagner’s reagent Brown or reddish brown colour shows presence of alkaloids.
- 30. 5. Tannic acid test- Test- Drug extract+5% tannic acid solution- Buff colour ppt. shows presence of alkaloids.
- 31. Extraction, Purification and Isolation of Alkaloids from Powdered plants ➢ Extraction and purification Method I: The powder is treated with alkalis to liberates the free bases that can then be extracted with water immiscible organic solvents. Method II: The powdered material is extracted with water or aqueous alcohol containing dilute acid. Alkaloids are extracted as their salts together with accompanying soluble impurities. Method III: The powder is extracted with water soluble organic solvents such as MeOH or EtOH which are good solvents for both salts and free bases.
- 33. ➢Liberation of the free bases: Alkalis are used to liberate free bases. Alkalis must be strong enough to liberate free bases. However, choice of strong alkalis must be avoided in some cases: 1- Ester Alkaloids e.g. Solanaceous Alkaloids 2- Amide Alkaloids e.g. Colchicine 3- Phenolic Alkaloids e.g. Morphine 4- Lactone Alkaloids e.g. Pilocarpine 5- Fatty Drugs due to saponification and emulsion formation.
- 34. ➢NH4OH: Most widely used due to many advantages: 1- Strong enough to liberate most of alkaloids from their salts. 2- Milder than fixed alkalis so more safe. 3- Volatile so easy to get rid of it. ➢Other Alkalis: Na2CO3, NaHCO3, Ca(OH)2, MgO.
- 35. Identification of Alkaloids: ➢Melting point ➢Colour test ➢Optical Rotation ➢Microcrystal test ➢HPLC, GC, GC-MS ➢UV, IR, NMR, MS.