Bioisosterism

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Chapter: Medicinal Chemistry : Bioisosterism

Isosterism is of vital importance to the medicinal chemists because the biological characteristics of isosteres appear to be similar; more frequently than physical or chemical characteristics.


Bioisosterism

INTRODUCTION

Isosterism is of vital importance to the medicinal chemists because the biological characteristics of isosteres appear to be similar; more frequently than physical or chemical characteristics. Keeping in view the numerous advantageous application of isosterism in resolving biological problems effectively, Friedman proposed the following definition of bioisosterism—the phenomenon by which compounds usually fit the broadest definition of isosteres and possess the same type of biological activity.

For instance, among antihistamines it is always preferable to have small compact substituents on the terminal nitrogen.


In the above-mentioned three structural analogues, it has been observed that ‘A’ possesses twice the activity of ‘C’, whereas it showed an activity that is many times greater than that of the open-chain diethylamino analogue.

It has been duly observed that it is more or less difficult to correlate the biological properties vis-à-vis physicochemical properties inherited by specific individual atoms, functional groups, or entire molecule by virtue of the glaring and established fact that a host of physical and chemical parameters are involved simultaneously, and are, therefore, extremely difficult to quantify them justifiably.

Besides simpler relationships, for example, isosterism invariably do not delay across the several varieties of biological systems that are often encountered with medicinal agents. In other words, a specific isosteric replacement in one particular biological system may either work or fail in response to the other. Thus, bioisosteres were further explained as follows: bioisosteres are (functional) groups or molecules that have chemical and physical similarities producing broadly similar biological properties.


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