Bioisosteres – A bioisostere is a molecule resulting from the exchange of an atom or of a group of atoms with an alternative, broadly similar, atom or group of atoms. The objective of a bioisosteric replacement is to create a new molecule with similar biological properties to the parent compound. The bioisosteric replacement may be physicochemically or topologically based. The replacement can attenuate toxicity, modify activity of lead, and/or alter pharmacokinetics or the toxicity of the lead. The order in which bioisosteres are described does not imply any preference, all substituents are often interchangeable. It should be noted that often it is not possible to simply replace one halogen with another, bonds to halogen are significantly weaker than hydrogen bonds and there are significant differences in the nature of the interaction.

Worth reading 

Synopsis of Some Recent Tactical Application of Bioisosteres in Drug Design DOI

Bioisosteres in Medicinal Chemistry (Methods and Principles in Medicinal Chemistry

Applications of Deuterium in Medicinal Chemistry DOI

A Data-Driven Perspective on Bioisostere Evaluation: Mapping the Benzene Bioisostere Landscape with BioSTAR DOI

SwissBioisostere: a database of molecular replacements for ligand design DOI

 SwissBioisostere is a web service designed to give ideas about potential bioisosteres, this is derived from a matched molecular pair (MMP) analysis of ChEMBL 17. Two different queries are possible: You are interested in a range of possible replacements for a single substructure ( e.g. replacements for an amide group ); or you want to know details about a particular substructural replacement of interest ( e.g. carboxylic acid vs. tetrazole ). Whilst this is very comprehensive it contains a lot of transformations that were never intended to be bioisosteric replacements.