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PLANT GLYCOSIDES

PLANT GLYCOSIDES. Glycoside Definition. A substance which on hydrolysis yields a reducing sugar + one or more non-sugar substances ( genin/aglycone ) Normally aromatic in nature Known as the aromatic aglycone or genin portion. Glycosides. Glycoside = Broad & general term

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PLANT GLYCOSIDES

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  1. PLANT GLYCOSIDES

  2. Glycoside Definition A substance which on hydrolysis • yields a reducing sugar • + one or more non-sugar substances (genin/aglycone) • Normally aromatic in nature • Known as the aromatic aglycone or genin portion

  3. Glycosides • Glycoside = Broad & general term • Embraces all the many various combinations of sugars & aglycones • e.g. Cardiac glycosides, flavonoid glycosides, phenolic glycosides etc.

  4. In nature: Formed by the interaction of the nucleotide of a sugar group with the alcoholic or Phenolic group of a 2nd compound. This glycoside is called an O-glycoside Most numerous kind found in nature Glycoside Formation

  5. Other glycosides occur through sulphur links Called S-glycosides Nitrogen links Called N-glycosides Through Carbon links Called C-glycosides Other Glycoside Formation NOTE:Reactions for both the formation and Hydrolysis of glycosides are reversible

  6. Glycosidal Reduction • Glycosides themselves do not reduce Fehling’s solution, But the simple sugars they produce on hydrolysis (aglycones) do (precipitate red cuprous oxide)

  7. Glycosidal Sugars • Sugars found in glycosides may be • Monosaccharides • Glucose • Rhamnose • Fructose • Deoxysugars (more rare) • Cymarose • E.g. those found in the cardiac glycosides

  8. Terms used to Describe Glycosides A Glycoside is a • Glucoside • Has glucose as the sugar component • Pentoside • Has a sugar such as arabinose • Rhamnosides • Contains rhamnose • Rhanmoglucosides • Contains both rhamnose and glucose

  9. Terms used for Aglycones • Normally self-explanitory • E.g. Phenol • Anthroquinone • Sterol glycoside

  10. Other Glycosidal Terms • saponin (soap-like) • Cyanogenic (producing hydrocyanic acid) • Cardiac (having an action on the heart) • Terms: Are used to group glycosides together which have similar functions & chemical structure.

  11. GLYCOSIDE STRUCTURE • 2 types of genin are distinguished • Based on the structure of the lactone ring • 5-membered ring  bufanolides or bufadienilolides • E.g. scillarenin • 6-membered ring  cardinolides or cardiac active glycosides (medicinally more significant)

  12. A small group of plant glycosides act directly on the heart muscle. These include (but are not limited to cardiac glycosides or cardenolides) Cardenolides are steroidal glycosides exert a slowing and strengthening effect on the failing cardiac muscle. Cardio-Active Glycosides

  13. Cardenolide

  14. E.g. Digitalis purpurea (Purple Foxglove). Other uses of the plant (and glycoside) include being used as arrow poisonings. Cardiac Glycosides

  15. Pharmacological Action of Cardiac Glycosides • Effectiveness depends on both the aglycones and the sugar attachments. • Medicinal action depends on the aglycone • But the sugars make the compound more soluble in increases the fixation of the glycoside to the heart muscle

  16. Pharmacological Action of Cardiac Glycosides • The overall action of Digitalis glycosides is complicated by the number of different effects produced. • The exact mode of action on the myocardial muscle still needs investigation. • It is thought to act in competition with K ions for specific receptor enzymes (ATPase) sites in the cell membranes of the heart muscle when there is an influx of Na ions. • Effect is to increase the force of heart contraction • Diuretic action relates to the improved circulatory effects.

  17. Description: A perennial herb growing up to 1.5m with a single erect stem, broad lance-shaped leaves and bell-shaped, purple-pink or white flowers in long spikes History: The poisonous nature of the leaves are well known, and the drug was recommended for use since 1542. Discovered by William Withering, an 18th century country doctor (cardiac effect) His work led to the production of a life-saving medicine Digitalispuruperea – (Scrophulariaceae)

  18. Definition: Digitalis consists of the dried leaves of Digitalispurpurea. It is required to contain at least 0.3% of total cardinolides calculated as digitoxin. Digitalispurpurea – Purple Foxglove

  19. Digitalispurpurea • Parts Used: • Leaves • Habitat: Native to Western Europe. Although the plant is cultivated, wild plants are thought to be superior. • Collection: • First or second-year leaves are permitted. • After collection the leaves should be dried as soon as possible at a temperature of about 60ºC. • Stored in airtight containers & protected from light. • Moisture content should be no more than 6%.

  20. Digitalispurpurea - Collection • There is a general belief that the pharmacological activity of the leaves increase during the course of the day to reach a maximum in the early afternoon (when they should be harvested). • This was supported by assays done in 1956 which showed a greater activity of the leaves at noon than 8am, irrespective of if the leaves where in the sun or shade. • However, other work indicates that there is no glycosidal content variation of the leaves when measured at 3-hour intervals.

  21. Stomata and hairs present on both surfaces (more on lower surface) No calcium oxalate Clothing hairs are uniseriate Glandular hairs Microscopical Characteristics

  22. Active Constituents • glycosides • purpurea glycoside A • purpurea glycoside B • (2 main actives in the fresh leaf) • Glucogitaloxin • At C-3 of the genin: a linear chain of 3 digitoxose sugar moieties terminated by glucose

  23. On drying: enzyme degradation takes place  loss of the terminal glucose. Produces Digitoxin Gitoxin Gitaloxin (main actives in dried leaves) Poor storage leads to further hydrolysis and complete loss of action Active Constituents

  24. Digitalis – Active Constituents • also contains anthraquinone glycosides • Saponins • Sopogenins • Flavonoids

  25. Active Constituents • Other glycosides (present in smaller quantities) include • Digitalose • Glucose • Verdoxin (x3 more toxic than gitaloxin)

  26. Digitalis – Active Constituents • It is generally agreed that the first-year leaves collected in Jan-Feb (Southern Hemisphere) have the highest content of total glycosides. After that they decrease during the winter months. After that another peak is reached during the time of flowering, but not as high as the first one.

  27. Digitalis – Medicinal Actions • tonic effect on the diseased heart • glycosides enable the heart to beat more strongly, slowly and regularly, without using or needing more O2. • Stimulates urine production  lessening the load on the heart.

  28. NB! • Kellar-Keliani Test for digitoxise Pg 509/Pg146

  29. Allied Drugs D. thaspi D. lutea D. ferruginia Adulterants Verbascum thapsus (mullein leaves) Symphytum officinalis (Comfrey) Primula vulgaris (Primrose) Inula helenium (elecampane) Urtica dioica (stinging nettle) Digitalispurpurea

  30. Digitalis purpurea • Cautions • Potential for overdose • Only under professional supervision • Plant is subject to legal restrictions.

  31. Digitalis lanata – Woolly Foxglove Today’s main source of cardiac glycosides • Self-study: Pg 147-9

  32. Cardioactive properties Similar to Digitalis, but less cumulative Therefore sometimes preferred rather than Digitalis (tolerated better, fewer side effects) Therapeutic Action: Heart stimulant Convalariamajalis – (Liliaceae)

  33. Parts used: Collected parts include aerial parts (when flowers begin to open) rhizomes & roots Convallariamajalis – lily of the valley

  34. Glycosides (highest in flowering period) Convallatoxin On hydrolysis give Strophanthidin & (-) – rhamnose minor cardinolides (±40 glycosides) Convalloside (seed) Convallatoxol Saponins – convallamaroside Flavonoids Convallatoxin Molecular Formula: C29H42O10 Convallariamajalis – Constituents

  35. strengthens contraction of heart muscle lowers internal heart pressure increases cardiac efficiency venotonic Convallaria – Pharmacological Effects

  36. very toxic only administered by professionals. may cause nausea, vomiting & GIT symptoms if taken in large amounts Because Convallaria cardenolides are poorly absorbed in the stomach and intestines they are rarely deadly. Convallaria - Cautions

  37. Part Used: Dried seeds (ripe) Habitat: East Africa. Greek strophos (a twisted cord or rope) anthos (a flower) Strophanthuskombe

  38. Constituents Strophanthoside strophanthin cymarin all based on genin - strophanthidin) Alkaloid: Inoeine Fixed oil, resin mucilage Strophanthin Glycoside Molecular formula: C29H44O12 Strophanthuskombe

  39. Uses - similar toDigitalis Chronic cardiac weakness Diuretic action (thought to be more powerful than Digitalis) Can be administered IV Actions Similar to Digitalis POISONOUS Strophanthuskombe

  40. Read • Oleander Glycosides – Pg 149

  41. Bufadienolides • Less commonly distributed in nature than cardenolides • Occur in some Liliaceae and Ranunculaceae Species. Also occur in toad venoms. • Therapeutically there is not much value as the therapeutic index is low and production of side effects high. • Squill, however has a time-honoured place as an expectorant • Widely used in the treatment of cough.

  42. Bufadienolide

  43. Definition: Consists of the dried sliced bulbs of Urgineamaritime, from which the membranous outer scales have been removed. It is commercially known as white squill. Description: A perennial herb growing up to 1.5 m from a large white (or red) bulb. It has a single flowering stem, a rosette of large basal leaves, and a dense spike of white flowers. Urginea maritima – (Liliaceae)

  44. Parts used: Bulbs Collection & Preparation: The bulbs are collected when the plant is finished flowering and has no aerial leaves. The dry outer scales are removed Bulbs cut transversely into thin slices Then dried in the sun or by stove heat. When 80% of the wt is lost, they are packed into bags/barrels. Urginea maritima - Squill

  45. History Squill appears in Egyptian Ebers papyrus (1500BC) In Greece it was used by Pythagoras & Hippocrates in the 6th & 5th centuries BC. Urginea maritima - Squill

  46. Microscopical Characteristics mucilage calcium oxalate small starch grains stomata are absent or rare (wide guard cells) Constituents Glycosides Scillaren A (most NB) Scillaren B Urginea maritima - Squill

  47. Actions & Uses glycosides are poorly absorbed in GIT  short action duration (not cumulative) In small doses: mild gastric irritation causing a reflex secretion of bronchioles Reflex expectorant action Larger doses: emetic Diuretic Cardiotonic Urginea maritima - Squill

  48. Cautions: Only under professional supervision. Toxic in excessive doses Unofficial varieties Red Squill – contains squilloriside – very toxic Indian Squill – Urginea indica Urginea maritima - Squill

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