Alkaloids lecture 1 (Introduction)
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This document provides an overview of alkaloids, which are basic nitrogenous plant compounds that often have physiological effects. It discusses the definition, functions, nomenclature, classification, physical and chemical properties, qualitative tests, isolation, and quantitative assay of alkaloids. Key points covered include that alkaloids can act as protective agents in plants or be metabolic byproducts, are classified based on origin and structure, undergo reactions like dehydration with acids, and can be isolated from plants and quantified.
![[The colors formed
are characteristic.
The tests are
sensitive to micro
amounts and can be
used for colorimetric
assay]
Ammonium molybdate/conc.
H2SO4
Ammonium vanadate / conc.
H2SO4
Formaldehyde / conc. H2SO4
Conc. nitric acid / conc. H2SO4
Potassium bismuth iodide
Color reagents:
1.Froehd's
2.Mandalin's
3.Marquis'
4.Erdmann's
5.Dragendorff's
Coloring reagents](https://image.slidesharecdn.com/alkaloids1-160215123735/85/Alkaloids-lecture-1-Introduction-30-320.jpg)
Alkaloids lecture 1 (Introduction)
- 2. Objectives ■ Definition ■ Function ■ Nomenclature ■ Classification ■ Physical properties ■ Chemical properties ■ Qualitative chemical tests ■ Isolation ■ Quantitative chemical assay
- 3. Definition: Alkaloids, which means alkali-like substances , are basic nitrogenous compounds of plant or animal origin and generally possessing a marked physiological action on man or animals. The nitrogen is usually contained in a heterocyclic ring system and it mainly derived from amino acids.
- 4. • Function of alkaloids in plants 1. They may act as protective against insects and herbivores due to their bitterness and toxicity. 2. They are, in certain cases, the final products of detoxification in metabolic reactions, therefore considered as waste products of metabolism. 3. They may provide nitrogen to the plant organs in case of nitrogen deficiency (source of nitrogen). 4. They, sometimes, act as growth regulators in certain metabolic systems. 5. They may be utilized as a source of energy in case of deficiency in carbon dioxide assimilation, especially those alkaloids containing a sugar moiety.
- 5. Some alkaloids are extremely poisonous e.g.: •Ergot alkaloids caused epidemic poisoning in the Middle Ages in Europe as a result of feeding on rye bread contaminated with the fungus. •The extracts of plants containing such alkaloids have long been used as arrow poisons in hunting and warfare e.g. curare extract that contains tubocurarine alkaloid. •Certain were employed in this respect, as a draught for execution e.g. Socrate’s execution, in ancient Greece, with hemlock which contains coniine.
- 6. •At the time of the Roman Empire, Belladonna (the source of atropine) has 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 and nicotine is responsible of the psychological and physical dependence of tobacco.
- 7. Nomenclature: Alkaloids terminate with the suffix-ine, their names may be derived from the: Genus name e.g., Atropine from Atropa. Species name, e.g., Cocaine from Coca. Common name, e.g., Ergotamine from Ergot. Physiological activity, e.g. Emetine (emetic). Discoverer, e.g., Pelletierine from Pelletier.
- 8. Prefixes and suffixes: Prefixes: "Nor-" designates N-demethylation e.g. Norpseudoephedrine and Nornicotine. "Apo-" designates dehydration e.g. Apomorphine. "Iso-, pseudo-, neo-, and epi-“ indicate different types of isomers. Nornicotine Nicotine Morphine Apomorphine
- 9. Suffixes: "-dine" designates isomerism as in the case of the Cinchona alkaloids, quinidine and cinchonidine are the optical isomers of quinine and cinchonine, respectively. N H H H HO H N R N H H H H HO N R (-)-Quinine R = OCH3 (-)-Cinchonidine R = H (+)-Quinidine R = OCH3 (+)-Cinchonine R = H Cinchona Alkaloids
- 10. Classification Different systems of classification based on: The pharmacological action (biological activity) The chemical structure (type of nitrogen, heterocyclic or non-heterocyclic and type of ring structure) The biochemical origin (biosynthetic pathway of production in the plant) The taxonomical origin (plant families rich in alkaloids)
- 11. Type of alkaloid Precursor Type of nitrogen True alkaloids Amino acids Heterocyclic Protoalkaloids Amino acids Non-heterocyclic Pseudoalkaloids Non-amino acids Heterocyclic According to Hegnauer’s classification, which is based on both the type of nitrogen and the biochemical origin, three main types of alkaloids are distinguished: •True alkaloids: these are derived from amino acids and have nitrogen in a heterocyclic ring. •Protoalkaloids: these are derived from amino acids and do not have nitrogen in a heterocyclic ring. •Pseudo alkaloids: these are not derived from amino acids but have nitrogen in a heterocyclic ring.
- 12. CLASSIFICATION OF ALKALOIDS 1) Pharmacological action (Biological activity) e.g. Morphine and CodeineAnalgesics e.g. Caffeine and StrychnineCNS stimulants e.g. Vincristine, Vinblastine and TaxolAnti-cancers e.g. AtropineMydriatics e.g. PilocarpineMyotics e.g. EphedrineAnti-asthmatics e.g. CodeineAnti-tussives e.g. LobellineExpectorants e.g. ReserpineAnti-hypertensives e.g. Atropine and PapaverineSmooth muscle relaxants e.g. TubocurarineSkeletal muscle relaxants e.g. PelletierineAnthelmintics e.g. Quinine and EmetineAntiparasitics
- 13. 2) Chemical structure A-types of nitrogen, Heterocyclic or non- heterocyclic B- according to type of ring structure. a) Non-Heterocyclic or atypical alkaloids * Sometimes called Protoalkaloids or Biological amines e.g. Ephedrine, Colchicine, and Taxol. * All have exocyclic N-atoms. b) Heterocyclic or typical alkaloids which sub- divided into several groups according to their ring structure.
- 14. Pyrrole NH Pyrrolidine Pyrrolizidine Pyridine Piperidine Tropane NH N NH N CH3 N Quinoline Isoquinoline Aporphine Indole Indolizidine Imidazole Purine N N N CH3 N H N H N N H N NN N
- 15. 3- Alkaloids are classified according to the amino acid that provides both the nitrogen atom and the fundamental portion of the alkaloid skeleton. Alkaloid skeletonAmino acid Pyrrolidine and tropane alkaloidsOrnithine piperidine, quinolizidine, and indolizidine alkaloidsLysine pyridine alkaloidsNicotinic acid phenylethylamines and simple tetrahydroisoquinoline alkaloids, Tyrosine simple indole, simple β-carboline, terpenoid indole, quinoline, pyrroloindole, and ergot alkaloids Tryptophan acts as a precursor to quinazoline, quinoline and acridine alkaloids Anthranilic acid imidazole derivativesHistidine
- 16. The Nitrogen atom in Alkaloids Number of nitrogen atoms: * The alkaloids must have at least one nitrogen atom in their structures * Alkaloids may contain more than one up to 5 nitrogen atoms e.g. Nicotine (2 N atoms), Ergotamine (5 N atoms).
- 17. Type of amino group: 1) A primary amino group e.g. Nor- pseudoephedrine. 2) A secondary amino group e.g. Ephedrine. 3) A tertiary amino group e.g. Nicotine and Atropine. 4) A quaternary ammonium ion e.g. Tubocurarine. Ammonia H N H H H N H R R2 N H R1 R2 N R3 R1 R2 N R4 R1 R3 Primary amine Secondary amine Tertiary amine Quaternary ammonium ion
- 18. Tubocurarine
- 19. Physical properties • Condition: Most alkaloids are crystalline solids. Some are liquids that are either: Volatile e.g. Nicotine and Coniine. Non-volatile e.g. Pilocarpine and Hyoscine. • Color: The majority of alkaloids are colorless but some are colored e.g.: Colchicine and Berberine are yellow.
- 20. 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 and psychotrine in ether, Theobromine and theophylline in benzene.
- 21. Salts are usually soluble in water and, insoluble or sparingly soluble in organic solvents. Exceptions: Salts insoluble In water: e.g. quinine monosulphate Salts soluble in organic solvents: e.g. Lobeline hydrochlorides soluble in chloroform.
- 22. Optical activity: ■ Many alkaloids are optically active due to the presence of one or more asymmetric carbon atom (chiral) in their molecule. ■ Optically active isomers show different physiological activities. ■ Usually, the l (-) isomer is more active than the d (+) isomer e.g.: l-ephedrine is 3 times more active than d-ephedrine l-ergotamine is 3 times more active than d-ergotamine.
- 23. Exceptions: ■ d-Tubocurarine is more active than the corresponding l- form. ■ Both quinine (l-form) and its d- isomer quinidine are active. ■ The racemic dl-atropine is physiologically active.
- 24. Chemical characters: • Basicity: The unshared electron pairs on the nitrogen atom is responsible for alkaloidal basicity.
- 25. • Strong basic alkaloids can form salts even with very weak acids. While weak bases require more acidic medium. • Amphoteric alkaloids (e.g. morphine, psychotrine and cephaline contain a phenolic group and narceine contains - COOH group)
- 26. • Effect of heat and acids on alkaloidal stability 1) Heat: Alkaloids generally decompose on heating while some of them sublime e.g. caffeine. 2) Acids: Cold conc. acids may cause dramatic changes (meanwhile heating with dil. acids may cause similar changes) e.g.:
- 27. Dehydration: Some alkaloids lose water molecule to from the anhydro-or apo alkaloids e.g. Morphine to Apomorphine, Atropine to Apoatropine. Demethylation: N -or O-demethylation of certain alkaloids can take place upon heating with mineral acids e.g.: Quinine, Narcotine, Codeine, and Papaverine.
- 28. Chemical properties ■ In addition to carbon, hydrogen and nitrogen, most alkaloids contain oxygen in their molecules. ■ Few alkaloids are oxygen-free such as nicotine and coniine. Salt formation ■ Due to their basic character, alkaloids with acids make salts. ■ Strong bases form salts with very weak acids. ■ Weak bases require stronger acids. ■ Dibasic alkaloids may form two series of salts. ■ Very weak bases form unstable salts, e.g. piperine, papaverine, narcotine and caffeine. ■ Amphoteric alkaloids (e.g. containing phenolic or carboxylic groups) can form salts with both acids and alkalis. ■ Alkaloids showing acidic characters do not form salts with acids e.g. ricinine.
- 29. Tests for detection and identification RemarksCompositionName of reagent Color of precipitate: Creamy white (positive with most alkaloids, except caffeine and dilute ephedrine). Reddish brown Yellow Orange-reddish brown Yellow precipitate Potassium-mercuric iodide Iodine in potassium iodide Saturated solution of picric acid Potassium bismuth iodide Potassium cadmium iodide Alkaloidal precipitants: 1.Mayer's 2. Wagner's 3. Hager's 4.Dragendorff's 5. Marmé's
- 30. [The colors formed are characteristic. The tests are sensitive to micro amounts and can be used for colorimetric assay] Ammonium molybdate/conc. H2SO4 Ammonium vanadate / conc. H2SO4 Formaldehyde / conc. H2SO4 Conc. nitric acid / conc. H2SO4 Potassium bismuth iodide Color reagents: 1.Froehd's 2.Mandalin's 3.Marquis' 4.Erdmann's 5.Dragendorff's Coloring reagents
- 31. Powdered plant material Petroleum ether Extract Fats 1- Alcohol 2- Concentration 3- CHCl3 4- Dilute acid Organic layer Neutral & weakly basic alkaloids & Non-alkaloidal impurities 1- NH4OH or Na2CO3 2-CHCl3 Organic layer Strongly basic alkaloids Basic aqueous layer Quaternary ammonium bases Acidic aqueous layer Salts of strongly basic alkaloids Defatted powder Total alkaloids & Non-alkaloidal impurities Extraction and separation of alkaloids of different basicity
- 32. 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 and extraction, after each increment, with organic solvent.
- 33. Quantitative analysis Quantitative determination of alkaloids in crude drugs, galenicals and pharmaceutical formulations is carried with the aim of: 1. Determination of the genuineness of the raw vegetable material. 2. Evaluation of the pant material for marketing. 3. Determination of the site of biosynthesis in the plant. 4. Selection of the best stage for collection of the plant material. 5. Evaluation of the stability and activity of a preparation. 6. Prevention of overdose and intoxication by potent alkaloids. 7. Determination of the bioavailability in different organs and tissues.
- 34. 1) Volumetric methods. a) Aqueous titration. b) Non-aqueous titration. 2) Gravimetric methods. 3) Colorimetric and spectrophotometric methods. Methods of alkaloidal gravimetric assay
- 35. Summary ■ Definition ■ Function ■ Nomenclature ■ Classification ■ Physical properties ■ Chemical properties ■ Qualitative chemical tests ■ Isolation ■ Quantitative chemical assay