ALKALOIDS

1. ALKALOIDS

2. Alkaloid: Difficult to define No definitive difference between an alkaloid and naturally occurring complex amines. Alkaloids: plant derived, are alkali and contain at least one N2-atom. They also normally have a significant physiological action on humans and animals. ‘Proto-alkaloid’/ ‘amino-alkaloid’ – applied to compounds which lack one or more of the properties of typical alkaloids. Other alkaloids which do not conform with the general definition are synthetic compounds not found in plants but are very closely related to natural alkaloids. Alkaloid Definition

3. Alkaloid Description Contains nitrogen - usually derived from an amino acid. • Bitter tasting, generally white solids (exception - nicotine is a brown liquid). • They give a precipitate with heavy metal iodides. • Caffeine, a purine derivative, does not precipitate like most alkaloids. • Alkaloids are basic - they form water soluble salts. Most alkaloids are well-defined crystalline substances which unite with acids to form salts. In plants, they may exist • in the free state, • as salts or • as N-oxides. • Occur in a limited number of plants. Nucleic acid exists in all plants, whereas, morphine exists in only one plant species.

4. Tests for Alkaloids • Most alkaloids are precipitated from neutral or slightly acidic solution by • Mayer's reagent (potassiomercuric iodide solution) Cream coloured precipitate. • Dragendorff's reagent (solution of potassium bismuth iodide)orange coloured precipitate. • Wagner’s reagent (iodine in potassium iodide)  red-brown precipitate • Hagers reagent (picric acid)  yellow precipitate • Caffeine does precipitate

5. Occur in bacteria (Pseudomonas aeruginosa) and rarely in fungi (pscilocin from hallucinogenic mushrooms). Some alkaloids occur in several genera from different species (caffeine), but most occur in closely related species. Some occur in certain families (hyoscyamine), while others occur only in a specific species (morphine). Rarely do plants contain more than 1 type of alkaloid. All alkaloids of one plant will have a common biogenenetic origin Occurrence, Distribution & Location of Alkaloids

6. Alkaloids occur in all plant parts, but are usually localized in one organ (e.g. the bark or seeds). Within the plant, [alkaloid] can vary widely from part to part – some parts may contain no alkaloids. Occasionally, different alkaloids also form in different parts of the plant. Alkaloid concentrations occur in wide ranges – e.g. Madagascan periwinkle contains 3g per (anti-cancer) alkaloids per tonne of leaves.

7. The N2 atom can either be 1º, 2º, 3º or 4º (quaternary). This N2 feature affects the alkaloid derivatives which can be prepared and the isolation procedures. The Nitrogen of Alkaloids

8. Physical-Chemical Properties of Alkaloids MW: 100 – 900 Most bases which do not contain O2 are liquid at room temperature (nicotine), while those that do are solids. In rare cases they are coloured. Most solid bases rotate the plane of polarized light, have high melting points. Normally are not soluble in water (occasionally slightly soluble). Soluble in apolar or slightly polar organic solvents. Soluble in concentrated hydroalcoholic solutions

9. The basicity of alkaloids depends on the availability of the lone pair of e- on the N2 atoms: e- donating groups enhance basicity, while e-withdrawing groups decrease it. Because some alkaloids have a carbonyl group on the amide, they can also be neutral (colchicine & piperine). Basicity is also influenced by steric constraints. Basic characteristic renders complex alkaloids unstable, so that in solution they are sensitive to heat, light & oxygen. Basic character of alkaloids also allows them to form salts with mineral acids (such as hydrochlorides, nitrates and sulphates) or inorganic acids (tartrates, sulfamates). Alkaloid salts are soluble in water and dilute alcohols. Solid salts can be conserved well and are a common commercial form of alkaloids.

10. Classification of Alkaloids Alkaloids have a large variety in their botanical & biochemical origin, in chemical structure and pharmaceutical action. Therefore, like flavonoids, a range of different classification systems exist for grouping alkaloids. They can therefore be classified according to their • Biological origin • Chemical structure - 2 divisions • i. Atypical/non-hetrocyclic alkaloids (protoalkaloids or biological amines) • ii. Typical/hetrocyclic alkaloids (divided into 14 groups according to their ring structure) • Biosynthetic pathway

11. Numerous methods can be used to name alkaloids Generic plant name – atropine from Atropa belladonna Specific name of the plant – cocaine from Erythroxylum coca. Common name of the herb – ergotamine from ergot (rye) Physiological action of the plant – emetine producing emesis Other – e.g. morphine derived from ancient Greek mythology – Morpheus – god of dreams Naming of Alkaloids

12. Extraction of Alkaloids Extraction is based on the basicity of alkaloids and on the fact that they normally occur in plants as salts (i.e.: on the solubility of bases and salts in water and organic solvents). Herbs often contain other materials which can interfere with extraction such as large amounts of fat, waxes, terpenes, pigments and other lipophilic substances (e.g by forming emulsions) – avoided by defatting the crushed herb (using petroleum ether and hexane)

13. Extraction method normally depends on the raw material, the purpose of extraction & the scale on which is to be performed. For research purposes: chromatography allows for quick and reliable results. If larger amounts of alkaloids need to be extracted, one of the following methods can be used. TLC plate Alkaloid Extraction

14. Extraction in an Alkaline Medium Step 1: Powdered, defatted herb is mixed with an alkaline aqueous solution. This displaced alkaloids from their salt combinations. Free bases are then extracted with organic solvents. Normally aqueous ammonia is used, but a carbonate solution is used when alkaloids contain fragile elements such as a ester or lactone. In some cases, e.g. Cinchona bark, a mixture of calcium hydroxide & sodium hydroxide should be used as the alkaloids are bound to tannins. Organic solvent: chloroform, dichloromethane or ethyl acetate – depends on the toxicity, safety, cost & ease of recovery and recycling of the solvent).

15. Industry: uses solid-liquid extractors based on the principle of counter-current extraction, such Soxhlet apparatus. The Soxhlet Apparatus

16. Organic solvent containing alkaloids (bases) is separated from residue & concentrated by distillation under pressure if needed. Solvent is stirred with an acidic aqueous solution: alkaloids go into the solution as salts. Impurities remain in the organic phase. Repeated until the organic phase no longer contains alkaloids. Many acids can be used (HCL, Sulfuric, citric, tartaric), but always in very dilute concentrations (1-5%) Extraction of Alkaloids: Step II

17. Aqueous solution of alkaloid salts is washed with an apolar solvent (hexane) Alkalinized with a base using an organic solvent not miscible with water. Alkaloids precipitate and dissolve in the organic phase. Extraction of aqueous phase continues till all alkaloids have moved into the organic phase (tested when Mayer’s reaction on the aqueous phase becomes negative). This purification step may be carried out in a separation funnel or in centrifugal extractors. Separation Funnel Alkaloid Extraction: Step III

18. Organic solvent containing alkaloid bases is decanted, freed from water traces (drying over anhydrous salt e.g. sodium sulphate) and evaporated under reduced pressure. A dry residue remains: total basic alkaloids. Kava Powder Final Step

19. 2 Methods possible Pulverized drug is extracted directly with acidified water Or Pulverized drug is extracted with acidified alcoholic or a hydroalcoholic solution. This is then followed by distillation under vacuum (eliminates that alcohol, leaving behind and acidic aqueous solution of alkaloid salts) Vacuum Distillation Alkaloid Extraction in Acidic Medium

20. In both cases: Results = aqueous solution of alkaloid salts needing purification. Purification achieved by • Alkalinizing solution & extracting bases with an immiscible organic solvent. • Selectively absorb the alkaloids contained in the solution on an ion exchange resin, then eluting them with a strong acid. • Precipitating the alkaloids as iodomercurates. The resulting alkaloids are recovered by filtration, dissolved in a mixture of water, alcohol and acetone and decomposed by passing through an ion-exchange resin.

21. Ion-Exchange Resin

22. All methods of alkaloid extraction yield impure compounds, so alkaloids therefore have to be separated. TLC and HPLC are most commonly used. Under the best conditions, alkaloids can be obtained by direct crystallization: simply by neutralizing the acidic extraction medium. Crystals of Hydrastine Isolation of Alkaloids

23. Large-scale extractions may be sent to a factory for purification & separation (for cinchona and cocoa alkaloids). Separation and final purification may be done using fractional precipitation or fractional crystallization of salts. Chromatograpy is used for complex alkaloids and if only small amounts of alkaloids are needed. Volatile liquid alkaloids (nicotine) are isolated by distillation – alkaloid is distilled off in steam. Nicotine is an important insecticide, and large amounts are prepared from the parts of the tobacco plant which is not used for tobacco manufacture Isolation of Alkaloids

24. CNS Action: stimulants (caffeine) or depressants (morphine) ANS: sympathomimetics (ephedrine) or sympatholytics (yohimbine, ergot alkaloids), parasympathomimetics (pilocarpine), anticholinergics (choline), ganglioplegics (nicotine). Also: local anesthetics (cocaine), defibrillation (quinidine), anti-tumour agents (ellipticine), anti-malarial (quinine), anti-bacterials (berberine), and amoebicides (emetine). Pharmacological Action & Uses

25. These actions lead to the extensive use of alkaloid containing herbs and drugs. Although some are used as galenicals (belladonna, datura, and henbane), most are used as starting materials for industrial extraction (morphine from poppy straw or opium, and quinine from Cinchona bark.

27. An obstetrician well known for his care of and research into multiple-birth pregnancies has found that dietary changes can affect a woman's chances of having twins, and that her overall chance is determined by a combination of diet and heredity. By comparing the twinning rate of vegan women, who consume no animal products, with that of women who do eat animal products, Gary Steinman, MD, PhD, an attending doctor at Long Island Jewish (LIJ) Medical Center in New Hyde Park, NY, found that the women who consume animal products, specifically dairy, are five times more likely to have twins. The study is reported in the May 2006 issue of the Journal of Reproductive Medicine, available May 20.The culprit may be insulin-like growth factor (IGF), a protein that is released from the liver of animals -- including humans -- in response to growth hormone, circulates in the blood and makes its way into the animal's milk. IGF increases the sensitivity of the ovaries to follicle stimulating hormone, thereby increasing ovulation. Some studies also suggest that IGF may help embryos survive in the early stages of development. The concentration of IGF in the blood is about 13 percent lower in vegan women than in women who consume dairy. Chances Of Having Twins Can Be Modified By Diet

28. Biogenesis of Alkaloids Alkaloids are produced in plants by basic substances and reactions well-known in organic chemistry. Biosynthetic origin cannot be discussed in general terms for all alkaloids, instead it has to be covered separately for each of the major groups of alkaloids

29. True alkaloids are based on an amino acid (pre-cursor). Only a few amino acids form the pre-cursors for all alkaloids: ornithine, lysine, phylalanine, tyrosine, tryptophan, histidine and anthranilic acid. Alkaloid formation may require the involvement of only one molecule of amino acid, or 2 molecules of the same AA, or less commonly, 2 molecules of different AA or else several molecules of the same AA. The formation starts with the formation of a Schiff base or a Mannich reaction. When the alkaloid has additional C-atoms, these play important roles in other metabolic pathways.

31. Main Pre-cursors for Alkaloids • Group 1: Aliphatic AA’s – ornithine & lysine * Pre-cursors to pyrrolidien, piperridine & tropane alkaloids • Aromatic AA – Phenylalanine, tyrosine, tryptophane c. Precursors of terpenes, steroids & polyketides – often together with the aliphatic or aromatic AA’s  result in alkaloids of mixed biosynthetic origin

33. Hetrocyclic Alkaloids Pyrrolidine Alkaloids Piperridine/pyridine Pyrrolizidine Tropane Alkaloids Quinoline Alkaloids Isoquinoline Alkaloids Opium Alkaloids Aporphine Norlupinane Ipecac Alkaloids Indole Alkaloids Indolizidine Imidazole Purine Alkaloids Protoalkaloids Steroidal Terpenoid

34. Tropane Alkaloids Derived from tropine and consist of mandelic, tropic or benzoic acid esters of tropine. Are very closely related to each other All have pronounced physiological actions. Natural alkaloids include Hyoscyamine Hyoscine Atropine Cocaine The above mentioned alkaloids occur within the Solanaceae family (except cocaine – from Erythroxylaceae family)

36. Atropine & Hyoscine Have the same structure – differ only in their optical activity. Also have different physiological actions Atropine – deadly nightshade, Atropa belladonna: dilates eye pupils, decreases sweating, produces stomach acid and saliva & relaxes smooth muscle (asthma and colic). Hyoscine – black henbane, Hyoscyamus niger: Limited influence on the CNS. Sedative Cocaine: Narcotic properties & local anaesthetic action (e.g. used in eye drops).

37. Hyoscine

38. Definition: Stramonium Leaf consists of the dried leaves or dried leaves and flowering tops of Datura stramonium. The drug should contain at least 0.25% alkaloids calculated as hyoscyamine. Common names: Stramonium leaf, Thornapple, Jimson or Jamestown weed Datura stramonium - Solanaceae

39. Main (Tropane) Alkaloids * Hyoscyamine Hyoscine (2:1) Younger plants: hyoscine – predominant alkaloid Also contains Atropine Larger stems contain little alkaloid, and drug should contain no more than 3% of stems with a diameter >5mm Datura stramonium - Constituents

40. ALLIED DRUGS Datura innoxia Datura metel (dried leaves are also curled and twisted – like D. stramonium), but are browner in colour. Datura sanguinea ADULTERANTS Xanthium, Carthamus and Chenopodium leaves (easily distinguished from original herb) Datura stramonium – Allied Drugs & Adulterants

41. Atropine: Stimulant on CNS Depresses nerve endings on the secretory glands and smooth muscle Hyoscine: lacks CNS stimulant action of atropine Sedative – motion sickness Atropine & Hyoscine: used in opthalmic practice to dilate the pupil of the eye. Uses of Datura stramonium

42. Definition: Hyoscyamus leaf consists of the dried leaves or dried leaves and flowering tops of Hyoscyamus niger. It should contain at least 0.05% alkaloids – hyoscyamine. Common names: Henbane Hyoscyamus niger - Solanaceae

43. Tropane Alkaloids Mainly Hyoscyamine Hyoscine (main constituent) Hyoscyamus niger - Constituents

44. Hyoscyamus albus (petiolate stem-leaves and pale yellow, non-veined petals – bottom left). Hyosycamus muticus (top right) Hyoscyamus pusillus Hyoscyamus aureus Hyoscyamus reticulatus (Indian henbane – bottom right) Hyoscyamus niger – Allied Drugs

45. Resembles belladonna and stramonium in action – only weaker. Higher hyoscine content – less likely to cause cerebral stimulation . Used to relieve spasm of the urinary tract Hyoscyamus niger - Uses

46. Definition: Belladonna herb consists of the dried leaves and flowering tops of Atropa belladonna, containing at least 0.3% alkaloids (hyoscyamine). Should not contain >3% stem >5mm in diameter. USP also allows A. acuminata in the Belladonna Leaf monograph. Atropa belladonna - Solanaceae

47. Main (Tropane) alkaloid Hyoscyamine Also contains Scopoletin Calcium oxalate Atropa belladonna - Constituents

48. ALLIED DRUGS Indian belladonna (Atropa acuminata) – yellow-brown flowers & brown-green leaves. Atropa baetica (yellow flowers and black berries) – endangered species ADULTERANTS Phytolacca decandra Ailanthus glandulosa Atropa belladonna

49. Used as a sedative To stop bodily secretions (e.g. saliva) Root preparations are used externally Atropa belladonna - Uses