Dealing with Tautomers when Searching for Compounds

By Jameed Hussain | Tuesday, September 11, 2018 - 18:42 UTC
Dealing with Tautomers when Searching for Compounds

A common operation that needs to be performed in the chemical industry is compound searching. We are all familiar with searching for things on the web using Google or items to buy on a shopping website. The same type of thing is core operation in chemistry – finding specific compounds of interest. 

There are a few types of searches that typically need to be performed when searching for compounds. These are:

  1. Exact compound searching – find the compound that exactly matches your drawn structure
  2. Substructure searching – find compounds where the drawn structure forms part of the retrieved structure
  3. Similarity searching – find compounds that are similar or “like” your drawn structure

Within Chemselector all the above searches (and more) are available. Most chemists will be familiar with the types of searches described above. What I’ll cover in this blog post is dealing with an issue we are all likely to come across at some point when searching – that is dealing with tautomers. 

Tautomers are isomers of a compound that can exist in equilibrium and are readily interconverted. One of the more famous examples, guanine, is shown below. When you are in the unfortunate situation where you need to search for guanine (or other tautomeric compounds) in a chemical database, care needs to be taken to make sure you draw the structure of guanine as it appears in the database. This is likely to be straight-forward in cases where you are familiar with how guanine is stored in the database. However, when this is not the case (eg. a 3rd party database) you probably need to try several tautomers of guanine, which as you can imagine is pretty inconvenient.


ChemSelector has an option called “Explore Tautomers” which can help in this case. What the option does is take your drawn structure, enumerate most (if not all) of the tautomeric states it can exist in and search using each one. Therefore, even if the compound exists in the database in a different tautomeric state than the structure you have drawn, it should be found. I carried an exact search for guanine in the eMolecules database (September 2018) with and without the “Explore Tautomers” option and the results are shown below.


The “Explore tautomer” option finds all the different tautomeric forms of guanine found in the eMolecules database – as you can see there are several. These are all essentially the same compound. An interesting side effect of doing this is that it expands the possible options of compounds to order – fingers crossed there may be a cheaper/better one available. 


Submitted by Bushra (not verified) on Tue, 09/18/2018 - 08:58 UTC

This is a very informative piece of writing and perfect for my nephew who is studying Chemistry at University. 

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