**4.2 Bioactive small molecules**

*Cheminformatics and Its Applications*

*3.1.2.7 Affinity-based methods*

*optimization methods, and hypothesis limitation.*

**Figure 4.**

**4. Target identification and characterization**

**4.1 Disease association and target validation**

associates a target with a disease [53].

constant temperature [48]. Thermal shift screening methods has allowed to identify compounds that interact with *Trypanosoma brucei* choline kinase (TBCK) and inhibit TBCK, a validated drug target against African sleeping sickness [49].

*Comparison between the advantages and disadvantages of target-based and phenotypic screening based upon the different features such as molecular target of disease, its mechanism of action, confirmation methods, SAR* 

The methods regarding affinity-based immobilized proteins have vital role in understanding the connections between small molecules and their biological targets [50]. Affinity-based technologies are divided into two groups: (1) direct detection of noncovalent macromolecule-ligand complex and (2) indirect detection of noncovalent macromolecule-ligand complex. The negative aspect of this approach is that it recognizes chemical entities basically based on their binding affinities for a target irrespective of whether or not the biological function of the target is affected. In the late 1980s, matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) techniques were used to analyze proteins and nucleic acids. Both phenotypic screening and target-based screening are comparable to each other in terms of benefits and drawbacks. This fact has been illustrated in **Figure 4**.

Target identification and elucidation of its action mechanism have played vital roles in probing small molecules and drug discovery. Target identification has been

Identification of the molecules and their underlying pathophysiological mechanisms contribute towards the discovery of targets that can be modulated therapeutically [52]. Each drug target is linked to a disease using integrated genome-wide data from a broad range of data sources. The target validation reveals the evidence that

based on biological and technologically advanced cell-based assays [51].

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Bioactive small molecules are preferred as lead structures for the target validation. These small molecules isolated from phenotypic screen play a crucial role in chemical biology [54, 55]. Many genomic, proteomic, and bioinformatic technologies have been developed for validation of the drugs.
