Introduction to alkaloids
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This document provides an overview of alkaloids. It defines alkaloids as basic, nitrogen-containing compounds found in plants. Alkaloids are classified in several ways, including by their chemical structure, biosynthetic pathway, pharmacological effects, and the taxonomic plant family they are found in. Methods for isolating and purifying individual alkaloids from crude mixtures are also described. The molecular modification of opioid alkaloids like morphine to enhance their medical usefulness is discussed. Finally, the document outlines some of the biological activities that alkaloids can have in plants and humans, ranging from protective effects to therapeutic applications to toxicity.
Introduction to alkaloids
- 1. Alkaloids PRESENTED BY: ROHIT PAL M PHARMA FIRST YEAR PHARMACEUTICAL CHEMISTRY
- 2. Content • General introduction • Classification • Isolation and purification • Molecular modification • Biological activity
- 3. General introduction • The term “alkaloid” (alkali-like) is defined as physiologically active basic compounds of plant origin, in which at least one nitrogen atoms forms part of a cyclic system. • The term alkaloid was coined by W. Meissner, a German Pharmacist in 1819.
- 5. 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.
- 6. Classification of alkaloids • 1. Chemical classification of alkaloids • 2. Taxonomical classification of alkaloids • 3. Pharmacological classification of alkaloids • 4. Biosynthetic classification of alkaloids
- 7. Biosynthetic classification of alkaloids (i) Indole alkaloids derived from tryptophan. (ii) Piperidine alkaloids derived from lysine. (iii) Pyrrolidine alkaloids derived from ornithine. (iv) Phenylethylamine alkaloids derived from tyrosine. (v) Imidazole alkaloids derived from histidine.
- 8. Chemical classification of alkaloids 1) Phenylethylamine : Ephedrine 2) Pyrrolidine: Hygrine, stachydrine 3) Pyridine or piperidine: Lobeline, nicotine, piperine, conine, trigonelline 4) Pyridine-pyrrolidine: Nicotine 5) Tropane: Cocaine, atropine, hyoschyamine, hyoscine 6) Quinoline: Quinine, quinidine, cinchonine, cinchonidine
- 9. 7) Isoquinoline: Morphine, codeine, papaverine, norcotine, tubocurarine, emetine 8) Phenanthrene: Morphine, codeine, thebaine 9) Indole: Reserpine, ergometrine, strychnine, Yohimbine, serpentine, physostigmine 10) Tropolone: Colchicine 11) Imidazole: Pilocarpine, pilosine 12) Steroidal: Conessine, solanidine 13) Purine: Caffeine, theobromine 14) Terpene: Aconitine
- 10. Pharmacological classification of alkaloids • Interestingly, the 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, such as: analgesics, cardio-vascular drugs, CNS-stimulants and depressants, dilation of pupil of eye, mydriatics, anticholinergics, sympathomimetics, antimalarials, purgatives, and the like. However, such a classification is not quite common and broadly known.
- 11. Examples • (i) Morphine as Narcotic analgesic; • (ii) Quinine as Antimalarial; • (iii) Strychnine as Reflex excitability; • (iv) Lobeline as Respiratory stimulant; • (v) Boldine as Choleretics and laxatives; • (vi) Aconitine as Neuralgia; • (vii) Pilocarpine as Antiglaucoma agent and miotic; • (viii) Ergonovine as Oxytocic; • (ix) Ephedrine as Bronchodilator; • (x) Narceine as Analgesic (narcotic) and antitussive.
- 12. Taxonomic Classification • This particular classification essentially deals with the ‘Taxon’ i.e., the taxonomic category. The most common taxa are the genus, subgenus, species, subspecies, and variety. Therefore, the taxonomic classification encompasses the plethora of alkaloids exclusively based on their respective distribution in a variety of Plant Families, sometimes also referred to as the ‘Natural order’. A few typical examples of plant families and the various species associated with them are stated below, namely:
- 13. • (i) Cannabinaceous Alkaloids: e.g., Cannabis sativa Linn., (Hemp, Marijuana). • (ii) Rubiaceous Alkaloids: e.g., Cinchona Sp. (Quinine); Mitragyna speciosa Korth (Katum, Kratum, Kutum); Pausinystalia johimbe (K. Schum) (Yohimbe). • (iii) Solanaceous Alkaloids: e.g., Atropa belladona L., (Deadly Nightshade, Belladona); Capsicum annuum L., (Sweet Peppers, Paprika); Datura candida (Pers.) Saff. (Borrachero, Floripondio) etc. • Invariably, they are grouped together according to the name of the genus wherein they belong to, such as: coca, cinchona, ephedra.
- 15. Isolation of alkaloids • The resulting crude alkaloid mixture is separated into individual alkaloids by means of fractional Crystallization, fractional precipitation, column chromatography, partition chromatography, Gas chromatography or counter current extraction.
- 17. Molecular modification • Molecular modification is chemical alteration of a known and previously characterized lead compound for the purpose of enhancing its usefulness as a drug. • Medicinal chemistry is a chemistry-based discipline, involving aspects of biological, medical and pharmaceutical sciences. • It is concerned with the invention, discovery, design, identification and preparation of biologically active compounds, the study of their metabolism, the interpretation of their mode of action at the molecular level and The construction of structure-activity relationships (SARs).
- 18. Molecular modification of opioid alkaloids • The term opiate refers to compounds structurally related to products found in opium, a word derived from opos, the Greek word for “juice,” natural opiates being derived from the resin of the opium poppy, Papaver somniferum. • Opiates include the natural plant alkaloids, such as morphine, codeine, thebaine, and many semisynthetic derivatives.
- 19. Morphine as lead • Biological activity of opioids • Depends on
- 22. SAR - Methyl group on nitrogen • Nitrogen is essential for binding • The pure opioid antagonist drugs naloxone, naltrexone, and nalmefene are morphine derivatives with bulkier substituents at the N17 position. • These agents have a relatively high affinity for μ-opioid binding sites. They have lower affinity for the other receptors but can also reverse agonists at δ and κ sites.
- 23. Summary of SAR • Of course, thousands of compounds related to the morphine structure have been prepared and many without activity, and no compound has been found to halt the terrible addictive morphine properties. • When Used correctly, the morphine family is an important class of analgesics, and their study represents an important contribution to the understanding of medicinal activity.
- 30. Biological activity • In Plants • They may act as protective against insects and herbivores due to their bitterness and toxicity. • They are, in certain cases, the final products of detoxification (waste products). • Source of nitrogen in case of nitrogen deficiency. • They sometimes act as growth regulators in certain metabolic systems. • They may be utilized as a source of energy in case of deficiency in carbon dioxide assimilation.
- 31. In Humans • High biological activity. • Produce vary degrees of physiological and psychological responses – largely by interfering with neurotransmitter. • In large doses – highly toxic – fatal. • In small doses – many have therapeutic value. • Muscle relaxant, pain killers, tranquilizers, mind altering drugs, chemotherapy.