Exploring the Fascinating World of Alkaloids

Alkaloids Alkaloids Dr. Rakesh Pandey Assistant Professor Department of Botany

Introduction: Introduction: The term alkaloids was first used by Carl F.W. Meissner, a German pharmacist in 1819. Its name has been derived from an Arabic word al qu lja which translates into 'ashes of plants . They are basically a group of secondary metabolites of plant origin. Alkaloids can be defined as a group of naturally occurring organic compounds which are basic in nature and have atleast one or more nitrogen atoms in their heterocyclic structure. Cinchona calisaya

Most alkaloids are poisonous in nature( at high concentration) but show diverse and importantphysiological effects when taken atlowconcentration. Majority of alkaloids are synthesized from amino acids. The first alkaloid to be isolated and crystallized was morphine from opium by Friedrich Sert rner in 1804. Some of the important alkaloids are morphine, strychnine, quinine, ephedrine , nicotine, etc.

Sources and distribution of Alkaloids: Sources and distribution of Alkaloids: They are naturally produced mainly by higherplants. They are also produced by bacteria, fungi and animals. Around 5000alkaloids are known to occur in 15% of alllandplants from 150 families. It is present in various parts of plant such as: 1. Aerial part- Ephedrine 2. Entire plant- Vincristine, Vinblastine 3. Leaves- Caffeine 4. Roots- Reserpine 5. Bark- Quinine 6. Seeds- Nuxvomica 7. Fruit- Piperine 8. Latex- Morphine, Codeine

In case of fungi, Ergot contain ergotamine , lisegic acid. Some gymnosperm species like Ephedra and Taxus also contain alkaloids like ephedrine, pseudoephedrine, taxine, etc. In angiosperms, families rich in alkaloids are: Dicots:Papaveraceae,Rubiaceae,Solanceae,Apocynaceae Fabaceae,Berberidaceae, Ranunculaceae, Rutaceae, etc. Monocots:Liliaceae, Amaryllidaceae,etc. Occurrence: Alkaloids occur mainly in plants as salts of organic acids such as oxalic acid, citric acid, acetic acid, maleic acid, tartaric acid, fumaric acid, benzoic acid ,etc. Ergot Ephedra sinca

List of some Alkaloids along with their sorces: List of some Alkaloids along with their sorces:

Types of Alkaloids Types of Alkaloids: (Based on origin) 1. True Alkaloids 2. Proto Alkaloids (Amino Alkaloids) 3. Pseudo Alkaloids 1. Contain Heterocyclic N- atom ( N in Heterocyclic ring). 1. Contain N but not in ring system ( Heterocyclic ring). 1. Contain Heterocyclic N- atom. 2. Derived directly from amino acid ( tryptophan, tyrosine, phenylalanine, lysine, ornithine, histidine,etc.) 2. Derived from amino acid. Sometimes considered as Biological amine. 2. Arenot derived from amino acid i.e., derived from non-amino acid precursors. 3. Basic in nature; forms water-soluble salts. 3. Basic in nature 3. Weakly basic nitrogenous compounds. Examples: Quinine, Atropine, Morphine. Examples: Colchicine, Ephedrine. Examples: Caffeine, Solaridine.

Classification of Alkaloids: Classification of Alkaloids: There are different systems of classification based on: 1. The pharmacological action (biological activity) 2. The chemical structure (type of nitrogen, heterocyclic or non- heterocyclic and type of ring structure) 3. The biochemical origin (biosynthetic pathway of production in the plant) 4. The taxonomical origin (plant families rich in alkaloids)

Pharmacological Classification of Alkaloids: Pharmacological Classification of Alkaloids: Alkaloids exhibit a broad range of very specific pharmacological characteristics. Perhaps this might also be used as a strong basis for the general classification of the wide-spectrum of alkaloids derived from the plant kingdom. S.no. Properties Examples S.no. Properties Examples 1. Analgesics and Narcotics Morphine and Codeine 9. Smooth muscle relaxants Atropine and Papaverine 2. CNS-stimulants Caffeine and Strychnine 10. Skeletal muscle relaxants d-tubocurarine 3. Anti-cancer Vincristine and Vinblastine 11. Anthelmintics Pelletierine and Areoline 4. Mydriatics Atropine 12. Antiparasitics Quinine and Emetine 5. Bronchodilator Ephedrine 13. Choleretics Boldine 6. Antitussive Codeine 14. Neuralgia Aconitine 7. Expectorants Lobeline 15. Anti-glaucoma Pilocarpine 8. Anti-hypertensive Reserpine 16. Oxytocics Ergonovine

Chemical Classification of Alkaloids: Chemical Classification of Alkaloids: According to the nature of N-atom alkaloids can be of two types: A. Atypical alkaloids- They contain N-atom which is not a part of any ring system. For examples, Ephedrine, Colchicine and Taxol. B. Typical alkaloids- They contain N-atom in a heterocyclic ring. These are subdivided into several groups according to their ring structure. Some of them are: S.no. Heterocycle Examples 6. Indole or Benzopyrole Vinblastine, Vincristine, Strychnine, Reserpine 1. Pyrrole and Pyrrolidine Hygrine, Stachydrine 2 Pyridine and Piperidine Nicotine, Piperine 7. Imidazole Pilocarpine 3. Tropane Cocaine 8. Purine Caffeine 4. Quinoline Quinine 5. Isoquinoline Morphine, Papaverine, Strychnine, Reserpine 9. Steroidal Solanidine 10. Terpenoid Aconitine

Biosynthetic classification of Alkaloids: Biosynthetic classification of Alkaloids: Alkaloids are classified on the basis of types of precursor used for alkaloid biosynthesis in plant. Alkaloid biosynthesized by same precursor brought under same group. These include: Ornithine derived alkaloids- Nicotine ,Atropine, Cocaine Tryptophan derived alkaloids- Reserpine, Strychnine, Vincristine, Quinine, Cinchona Lysine derived alkaloids- Coniine, Lobaline Phenylalanine derived alkaloids- Ephedrine Tyrosine derived alkaloids- Morphine, Colchicine, Codeine, Berberine Histine derived alkaloids- Pilocarpine Alkaloids derived from substances other than amino acid- Caffeine, Theobromine.

Taxonomical Classification of Alkaloids: Taxonomical Classification of Alkaloids: This particular classification deals with the taxon i.e., the taxonomic category. In this classification, the alkaloids are grouped according to their respective plant families. Some of them are: 1. Apocynaceae- Reserpine, Serpentine, Vincristine, Vinblastine,etc. 2. Solanceae- Atropine, Hyoscyamine, Nicotine, Solanine, Cocaine,etc. 3. Papaveraceae- Morphine, Papaverine, Codeine, Narcotine, Thebanine, etc. 4. Rubiaceae- Quinine, Quinidine, Cinchonine, Cinchonidine, etc.

Physical Properties of Alkaloids Physical Properties of Alkaloids: 1. They are mostly crystalline solids; some are amorphous (e.g. Emetine) while some are liquid ( e.g. Nicotine and Coniine are volatile liquids whereas Pilocarpine is a non-volatile liquid). Majority of alkaloids are colourless; some are however coloured: Berberine, Colchicine yellow coloured Betanidine- orange coloured Free bases of alkaloids are soluble in organic non-polar solvents but insoluble in water. However, salts of alkaloids are soluble in water and sparingly soluble in organic solvents. Most of alkaloids are laevorotatory; few are dextrorotatory (e.g. quinine) and few are optically inactive (e.g. piperine) Sometimes, optically active isomers may show differentphysiologicalactivities. Most alkaloids are bitter in taste and many are poisonous. They have sharp melting points. 2. 3. 4. 5. 6. 7. 8.

Chemical Properties of Alkaloids: Chemical Properties of Alkaloids: 1. They are basic in nature due to presence of lonepairofelectrons on nitrogen atoms. 2. Their basic nature is enhanced if adjacent functional group is an electron releasinggroup. 3. Nitrogen in alkaloids may exist in the forms of: Primaryamines (RNH2) : Norephedrine Secondaryamines (R2NH) : Ephedrine Tertiaryamines (R3N) : Atropine Quaternaryammoniumion : Tubocurarine 4. Alkaloids are usually strong bases, however few can be amphoteric (e.g. Morphine) or neutral (e.g. Colchicine). 5. Alkaloids form salts when treated with organic acids. Lone pair of electrons

Functions of Alkaloids in plants: Functions of Alkaloids in plants: 1. They may act as protectiveagents 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 wasteproductsof metabolism. 3. They may provide nitrogen to the plant organs in case of nitrogen deficiency (sourceofnitrogen). 4. They, sometimes, act as growthregulators in certain metabolic systems. 5. They may be utilised as a source of energy in case of deficiency in carbondioxideassimilation, especially those alkaloids containing a sugar moiety.

Some Important facts about Some Important facts about Alkaloids: Alkaloids: Alkaloids are most notorious poisons inthe history of civilization. Coniine s (poisonous alkaloid) most famous victim is Socrates who was sentenced to death by poison chalice containing poisonhemlock. Curare is prepared by boiling the bark of one of the dozens of plant alkaloids sources, leaving a dark, heavy paste that can be applied to arrow or dartheads to make them poisonous. Ergot poisoning in humans and domestic animals is known as ergotism. This disease may cause strange hallucinations, the feeling of itchy and burning skin, gangrene, loss of hands and feet, and even death.

Prior to the development of wide range of relatively low-toxic synthetic pesticides, some alkaloids, such as salts of nicotine and anabasine, were used as insecticides. The plants in the human diet in which alkaloids are present are coffee seeds (caffeine), cacao seeds (theobromine and caffeine), tea leaves (theophylline, caffeine), tomatoes (tomatine), and potatoes (solanine). Alkaloids can be used as psychoactive substances or precursors for semi-synthetic psychoactive drugs.(e.g. cocaine, caffeine, cathinone,psilocybin, morphine, codeine etc. ) Alkaloids are the active principles of many abusive drugs like cocaine, opium etc.

References: References: B. Debnath, W.S. Singh, M. Das, S. Goswami, M.K. Singh, Role of plant alkaloids on human health: A review of biological activities, Materials Today Chemistry 9(2018) 56-72 Sarah E. O Connor, Alkaloids, Elsevier (2010) 977-1007 Jiao Peng, Ting-Ting Zheng, Xi Li, Yue Liang, Plant- Derived Alkaloids: The Promising Disease- Modifying Agents For Inflammatory Bowel Disease, Front. Pharmacol. (2019) 10:351. This content is only for educational purposes.