CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.8.1 Drugs from Natural Resources

Chirality & Drug Production

  • Chiral molecules are molecules that contain a carbon atom that is attached to four different atoms or groups of atoms
    • An example of a compound with a chiral centre is the CH3CHBrOH compound
  • A molecule with a chiral centre has to enantiomers which are non-superimposable mirror images of each other

An Introduction to AS Level Organic Chemistry Enantiomers and Chiral Centre, downloadable AS & A Level Chemistry revision notes

Examples of a molecule with a chiral centre

  • These enantiomers have similar chemical properties but differ from each other in their ability to rotate the plane of plane polarised light

Chiral drugs

  • Many drugs are derived from natural sources such as plants
  • The chiral drugs extracted from these natural sources often contain a single optical isomer only
  • An example of a drug derived from plants is the anti-cancer drug Taxol
  • Taxol has many chiral centres so many optical isomers of this single compound could exist
  • However, only one of these optical isomers is present in the bark of yew the tree which is extremely beneficial
  • In biological systems (such as cells), molecules are made and broken down by reactions involving biological catalysts called enzymes
  • Enzymes only bind molecules (substrates) that fit the shape of the enzyme’s active site by a lock-and-key mechanism
  • If the substrate molecule doesn’t have the correct shape, it will not bind to the enzyme 
  • Therefore, if there were many optical isomers (with each a different arrangement around the chiral centre) of the drug Taxol, they will no longer be able to fit the enzyme’s active site for a reaction to occur
  • Higher doses of the drugs would have to be administered for it to be effective
  • This is why it is so useful that natural sources (such as the yew tree) produce only one optical isomer

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Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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