3.4.1.2 Introduction of Double Bonds
The introduction of double bonds changes the stereochemistry of a molecule and
decreases the flexibility of carbon chains. The E and Z isomers may show very differ-
ent binding properties; for example, the ∆^1 -double bond of prednisone (3.7) increases
its activity against rheumatoid arthritis over that of its parent compound cortisol (3.8)
by about 30-fold. Decreasing molecular flexibility is also important in drug design. If a
drug molecule is too flexible, it will be able to fit into too many different receptors,
leading to undesirable effects and toxicity.
3.4.1.3 Variations in Ring Structure
Variations in ring structure are endless in drug synthesis, and are often used in the service
of some other change or are introduced simply for patent-right purposes. Inspection of
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