Secondary metabolites



Alkaloids, which means alkali like substances are basic nitrogenous compounds of plant and animal origin. They generally possess a marked physiological action on man and animals. The nitrogen is usually part of heterocyclic ring system and it is mainly derived from amino acids.


  1. Basically alkaloids are bitter in nature and it acts as insecticides inside the plant.
  2. At certain cases it also act as detoxification in metabolic reactions.
  3. They may provide nitrogen to the plant organ in case of nitrogen deficiency.
  4. They sometimes act as growth regulator in certain metabolic system.
  5. They may be utilized as a source of energy in case of deficiency in carbon dioxide assimilation, especially those alkaloids containing a sugar moiety.


Alkaloids ends with the suffix -ine. Their name may be derived from the:-

  • Genus name. Ex- Atropine from atropa
  • Species name. Ex- Cocaine from coca
  • Common name. Ex- Ergotamine from Ergot
  • physiological name. Ex- Emetine (emetic)
  • Discoverer. Ex- Pelletierine from Pelletier.


  1. Pharmacological action.
  2. Chemical structure.
  3. Biochemical origin.
  4. Taxonomical origin.

According to Hegnauer’s classification

This is bases on both the types of nitrogen and biochemical origin, three types of alkaloids are present

A. True alkaloids: These are derived from amino acids and have nitrogen in heterocyclic ring.