Alkaloids: Definition, Characteristics, Classification

Alkaloids are defined as a group of naturally occurring chemical compounds that mostly contain basic nitrogen atoms. mostly found in plants, that usually have a marked physiological (pharmacological) effect on humans and animals, even in small doses. They are typically basic in nature (because of the nitrogen), often bitter-tasting, and usually derived from amino acids.

. They have a unique property – an ability to work as either hydrogen-acceptor or hydrogen-donor for hydrogen bonding, depending on the type of amine functionality present in alkaloids. 

Examples of alkaloids

• Morphine
• Quinine
• Atropine
• Scopolamine
• Nicotine
• Caffeine
• Cocaine
• Reserpine
  

  For more details 
  Purine Alkaloids: Caffeine, Theophylline & Theobromine

  Tropane Alkaloids: Atropine, Hyoscyamine, Scopolamine & Cocaine

  Opium Alkaloids and Their Chemical Structures: A Complete

  
  General Characteristics of Alkaloids

  Most alkaloids have the following characteristics:

  • They contain nitrogen.
  • Many have a heterocyclic nitrogen-containing ring.
  • They are commonly produced by plants as secondary metabolites.
  • Many have a pronounced effect on the human body.
  • Many alkaloids are basic, although important exceptions exist.
  • Their free bases are often soluble in organic solvents, while their salts are generally more soluble in water.
  • They may occur in plants as salts of organic acids.
  • Many are pharmacologically active even in relatively small quantities.
  • They can be identified by chemical and chromatographic methods.

  
  

  Important point:
  Do not write that all alkaloids are strongly basic. Purine alkaloids such as caffeine are weakly basic or essentially neutral in ordinary acid-base behavior.