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Glycosides

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Glycosides Glycosides Secondary products formed from one or more sugar molecules added to a non-sugar biologically active molecule Sugar most commonly found is ... – PowerPoint PPT presentation

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Title: Glycosides


1
Glycosides
2
Glycosides
  • Secondary products formed from one or more sugar
    molecules added to a non-sugar biologically
    active molecule
  • Sugar most commonly found is glucose
  • Non-sugar molecule known as the aglycone and may
    be
  • amino acid derivatives
  • steroids
  • triterpenes

3
Glycosides
  • Most common types
  • Saponins
  • Cardiac Glycosides (Cardenolides)
  • Cyanogenic Glycosides
  • Anthraquinone Glycosides
  • Glucosinolates - technically not glycosides
  • Most glycosides function as deterrents to
    herbivores

4
Saponins
  • Terpene glycosides
  • Steroid glycosides
  • Steroid-alkaloid glycosides
  • Triterpene glycosides
  • May also occur as the aglycone and are called
    sapogenins

5
Properties of Saponins
  • Combination of hydrophobic terpene with a
    hydrophillic sugar produces cmpds that act as
    surfactants (detergents)
  • When agitated in water, saponins form a soapy
    lather

6
Effects of saponins on animals
  • Variable effects
  • Highly toxic to fish - used as fish poison
  • Not significantly toxic to mammals
  • Have a bitter acrid taste and cause severe
    gastric irritation if ingested
  • Implicated in livestock poisoning - alfalfa
  • Will hemolyze red blood cells if injected into
    blood stream - because of the detergent properties

7
Useful saponins
  • Saponins from yam - Disocorea spp. are the source
    of steroids used for human hormones
  • Birth control pills - most synthetic but some
    still use natural hormones
  • Anti-inflammatory steroids
  • Licorice - Glycyrrhiza glabra produces saponins
    that possibly help gastric ulcers because they
    suppress prostoglandins

8
Cardiac glycosides
  • Structurally similar to saponins with similar
    detergent properties
  • Distinguished by presence of a lactone ring and
    rare sugars
  • Wide distribution - found in over 200 species (55
    genera in 12 families)
  • Best known are digitoxin and digoxin from
    Digitalis (foxglove) 30 glycosides

9
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10
Digitoxin
11
Sugars in digitoxin
  • 2 molecules of digitose
  • 1 molecule of 1-acetyl digitose
  • 1 molecule of glucose

Digitose
12
Action of Cardiac Glycosides
  • In medicinal doses, cardiac glycosides increase
    the contractions of heart and the force of the
    heart beat
  • Increases cardiac output
  • Improved circulation, decreases edema, and
    increases kidney output
  • Most effective for congestive heart failure
  • Toxic doses cause arrhythmias or even cardiac
    arrest fine line between medicinal and toxic

13
Poisonous Plants with Cyanogenic Glycosides
  • Foxglove - Digitalis purpurea
  • Oleander - Nerium oleander
  • Lily of the Valley - Convallaria sp.
  • Milkweed - Asclepias spp

14
Oleander
15
Oleandrin
16
Milkweeds
  • Another common source of glycosides are milkweeds
    - produce latex rich in cardiac glycosides
  • Milkweed leaves host for monarch butterfly larvae
  • Glycosides sequestered in body of larvae and
    retained through metamorphosis and present in
    butterfly
  • Butterflies toxic to birds that feed on them
    causing vomiting - birds avoid butterflies

17
Cyanogenic glycosides
  • About 150 spp of plants produce glycosides that
    release hydrogen cyanide - HCN
  • Most cyanogenic glycosides are derived from 4
    amino acids (phenylalanine, tyrosine, valine, or
    isoleucine) or from nicotinic acid
  • Cyanogenic glycosides are not toxic by themselves
    but when a plant is damaged by an herbivore,
    glycoside is broken down by enzymes and HCN is
    released

18
Breakdown of cyanogenic glycosides
  • Two enzymes involved
  • b-glycosidase releases the sugars
  • Hydroxynitrile lyase releases HCN
  • Does not occur in intact plants because enzymes
    and substrates spatially separated (i.e.
    glycoside in epidermis and enzymes in mesophyll)
  • Only when cells crushed are they brought together

19
Effects of HCN
  • HCN inhibits ETS
  • HCN completely inhibits the transfer of electron
    to oxygen by cytochrome oxidase final step in
    the ETS
  • This can lead to cell death and possibly even the
    death of the organism if the concentration is
    high enough

20
Electron Transport System
21
HCN- Glycoside variability
  • Amounts of cyanogenic glycosides highly variable
    in any one species
  • Control of variability both genetic and
    environmental
  • Cassava (Manioc esculenta) major food crop with
    cyanogenic glycosides
  • Rosaceae (Rose Family) contains cyanogenic
    glycoside - amygdalin

22
Cassava glycosides
  • Traditional preparation removes toxins usually
  • In Africa reported cases of cassava paralysis due
    to HCN poisoning the motor region of brain

23
Cassava
24
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25
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26
Amygdalin
  • Found in seeds, stems, leaves and roots of
    apricots, cherries, peaches, apples, almonds -
    bitter almond
  • Acute poisoning has occurred when young children
    have eaten apricot pits
  • Laetrile - controversial cancer treatment

27
Laetrile
  • Apricot pits are rich in amygdalin
  • Ground up for preparation of laetrile, a
    controversial cancer treatment
  • Theoretically, laetrile releases HCN only in the
    presence of tumor cells and selectively destroys
    them
  • Not proven and laetrile not approved for cancer
    therapy in the United States

28
Amygdalin
29
Glucosinolates
  • Sulfur and nitrogen containing cmpds in the
    mustard family
  • Provide flavor of cabbages, broccoli,etc
  • Feeding repellants and insect toxins
  • Provide the potency of mustard and horseradish
    antibiotic properties of these
  • Rape seed development
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