Physicochemical Properties

Physicochemical Properties

INTRODUCTION

The biological activity of a targeted drug molecule is solely dependent on its physicochemical characteristics, essentially the nature and type of functional moieties, and also the spatial arrangement of such group in the molecule. Modulating the structure of a drug implies introduction, elimination, or substitution of certain groups in the drug. This may lead to the development of a parallel drug with the characteristic similar to the lead compound. Hence, the activity is maintained, although the structure is changed. This can be expressed by an idea of bioisosteric groups that generally have similar biological activity. Physicochemical properties play an important role in modifying the biological activities of many compounds. Thus, pharmacological or therapeutic effects of a drug also relate to its biodistributions or physicochemical parameters of a drug such as:

• hydrogen bonding

• chelation

• oxidation–reduction potential

• dissociation constant

• bioisosterism

• surface activity

Medicinal chemistry undoubtedly rests its main focus on the broad-based variations embracing the influence of numerous possible manipulations with regard to the chemical structure on the biological activity. In the light of the above statement of facts supported by copious volumes of scientific evidence reported in many of the literatures, it is almost important and necessary for the medicinal chemist to decipher and logically understand not only the ‘mechanism of drug action’ in vivo by which a drug substance exert its effect, but also the overall physicochemical properties of the molecule. In a rather most recent conceptualized theoretical basis, the terminology physicochemical characteristics invariably refer to the cognizable influence of the plethora of organic functional moieties strategically positioned within a drug substance. It is, however, pertinent to mention here that most of the aforesaid properties covertly and overtly exert a significant influence on the various biological phenomenons in vivo, such as absorption, distribution, metabolism, and excretion of newer targeted drug molecules.

Therefore, a creative medicinal chemist should ponder over the intricacies, complexities, and legitimate presence of each functional moiety to the overall physical and chemical properties of the targeted drug molecule with a view to arrive at or design safer, better, and efficacious medicinal agents. Nevertheless, such critical studies have to be carried out in a rather methodical and systematic manner vis-à-vis their effects upon biological activities.