Alkaloids

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Alkaloids
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Alkaloids

• Distribution
• Properties
• Role in plants
• Defense compounds
• Animal poisoning
• Lupine
• Groundsel
• Larkspur
• Jimson weed (Scopolamine)
• Henban (Atropine)
• Other roles in plants

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Lupines
Texas bluebonnet
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Effects of alkaloids on humans

• High biological activity
• Produce varying degrees of physiological and
  psychological responses - largely by interfering
  with neurotransmitters
• others interfere with membrane transport, protein
  synthesis or other processes
• In large doses - highly toxic - fatal
• In small doses, many have therapeutic value
• muscle relaxants, tranquilizers, pain killers,
  mind altering drugs, chemotherapy

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Psychoactive alkaloids

• Although only a small percent are psychoactive,
  these get much focus
• Affect the central nervous system - often by
  influencing neurotransmitters
• Categories of psychoactive cmpds
• Stimulants
• Hallucinogens
• Depressants
• May also be narcotic (addictive)

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Psychoactive alkaloids
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Alkaloid synthesis

• Most alkaloids are synthesized from a few common
  amino acids (tyrosine, tryptophan, ornithine or
  argenine, aspartic acid, lysine)
• Nicotinic acid precursor for part of nicotine
• Purine precursor for caffeine
• Some alkaloids synthesized from terpenes - along
  mevalonic acid pathway
• Generally classified by the predominant ring
  structure and/or carbon skeleton

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Tropane alkaloids
Many of these psychoactive alkaloids
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Pyrrolizidine alkaloids
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Piperidine alkaloids
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Piperidine/Pyridine alkaloids
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Purine alkaloids
Figure 3-5 Caffeine
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Quinoline alkaloids
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Isoquinoline alkaloids
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Indole alkaloids
Vindoline Vinblastine (Catharanthus)
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Quinolizidine alkaloids
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Steroidal alkaloids
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Steroidal alkaloids
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Diterpenoid alkaloids
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Amine alkaloids
Alkaloids without heterocyclic nitrogen atoms
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Other classes of alkaloids

• Betalain alkaloids - pigment alkaloids
• Lycopodium alkaloids - restricted to club mosses
• Peptide alkaloids