Essential Oils and Their Biological Application in Drug Discovery: Essential Oil as Potential Drug Leads

Introduction

Essential oils (EO) are complex mixtures of volatile secondary metabolites that are responsible for the aroma and biological properties of plants. The term “essential oil’ originated from the Latin expression ‘quintaessentia’ which literally means the 5^th element. Human interest on essential oils dates back to prehistorical periods where they are referred as the ‘soul or spirit’ of the plant. From time immemorial essential oils have find immense application in the treatment and management of acute and chronic diseases. They are extracted from various plant parts and exhibit diverse pharmacological properties (Table 34.1 & Figure 34.1). The use of EO to prevent illness and its utilization in religious ceremonies has been documented in historical records of several countries.

Figure 1.

Schematic representation of pharmacological properties of Essential Oil & their components

In plants, secondary metabolism produces a large number of specialized compounds, called secondary plant metabolites that play a vital role in plant health, defense, communication, signaling and in the regulation of primary metabolism. Albrecht Kossel, the Nobel Prize winner in 1910, first proposed the concept of secondary metabolites (SM) in plants. Based on biosynthetic pathway the SM is classified into: terpenoids, phenolic compounds, and alkaloids. Essential oils are composed on terpenoids, phenolics, alkaloids and a wide variety of aromatic and aliphatic compounds which include alcohols, aldehydes, ketones, that are present in variable concentrations.