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PLANT GLYCOSIDES

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

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Title: PLANT GLYCOSIDES


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
Glycoside Formation
  • 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

5
Other Glycoside Formation
  • Other glycosides occur through
  • sulphur links
  • Called S-glycosides
  • Nitrogen links
  • Called N-glycosides
  • Through Carbon links
  • Called C-glycosides

NOTE Reactions for both the formation and
Hydrolysis of glycosides are reversible
6
Glycosidal Reduction
  • Glycosides themselves do not reduce Fehlings
    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
Cardio-Active Glycosides
  • 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.

13
Cardenolide
14
Cardiac Glycosides
  • E.g. Digitalis purpurea (Purple Foxglove).
  • Other uses of the plant (and glycoside) include
    being used as arrow poisonings.

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
Digitalis puruperea (Scrophulariaceae)
  • 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

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

19
Digitalis purpurea
  • 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
Digitalis purpurea - 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
Microscopical Characteristics
  • Stomata and hairs present on both surfaces (more
    on lower surface)
  • No calcium oxalate
  • Clothing hairs are uniseriate
  • Glandular hairs

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
Active Constituents
  • 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

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
Digitalis purpurea
  • 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)

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

31
Digitalis lanata Woolly Foxglove
  • Todays main source of cardiac glycosides
  • Self-study Pg 147-9

32
Convalaria majalis (Liliaceae)
  • Cardioactive properties
  • Similar to Digitalis, but less cumulative
  • Therefore sometimes preferred rather than
    Digitalis
  • (tolerated better, fewer side effects)
  • Therapeutic Action Heart stimulant

33
Convallaria majalis lily of the valley
  • Parts used
  • Collected parts include
  • aerial parts (when flowers begin to open)
  • rhizomes roots

34
Convallaria majalis Constituents
  • 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

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

36
Convallaria - Cautions
  • 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.

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

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

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

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
Urginea maritima (Liliaceae)
  • Definition Consists of the dried sliced bulbs
    of Urginea maritime, 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.

44
Urginea maritima - Squill
  • 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.

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

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

47
Urginea maritima - Squill
  • 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

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