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
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. 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  Adulterants
 D. thaspi  Verbascum thapsus
 D. lutea (mullein leaves)
 D. ferruginia  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
Today’s 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  Convallatoxin
 On hydrolysis give  Molecular Formula:
• Strophanthidin C29H42O10
• & (-) – rhamnose
 minor cardinolides (±40
glycosides)
 Convalloside (seed)
 Convallatoxol
 Saponins –
convallamaroside
 Flavonoids

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