The introduction of a group in an unsubstituted position

The introduction of a new group may result in an increased rate of metabolism, a reduction in the rate of metabolism or an alternative route for metabolism (see Chapter 9). These changes could also change the duration of action and the nature of any side effects. For example, mono- and diortho-methylation with respect to the phenolic hydroxy group of paracetamol produces analogues with 

Example, the lead compound is given in square brackets([ ]) 

Increasing the number of CH2 groups in a chain can lead to micelle formation which can reduce drug activity (Fig. 4.1). Changing the number of CH2 groups in a ring may lead to a change in activity. 

Introduction of a double bond increases the rigidity of the structure and in some cases the possibility of E and Z isomers. The reduction of double bonds makes the structure more flexible. 

Introduction of a ring may result in the filling of a hydrophobic pocket in the target, which might improve the binding of the drug to its target. 

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