Focus on Synthetic Feasibility

The synthetically easiest way to access test compounds is to sample already available screening compounds, of which there are more than 10 million on the market. An approach on how to select commercially available materials has been described [54]. For example, a subset of less than 350 000 compoimds covering the same lead-like space as commercial compoimds from 10 major vendors has been generated [55]. 

Moving to in-house synthesis, there are a large number of proven synthetic protocols that have resulted in the actual synthesis of compounds, but the number of compounds synthetically accessible from these is, of course, much larger. Scientists at Pfizer have described an internal virtual library with about 10 members based on more than 1000 library synthesis protocols [25]. If there is structural understanding for a given target, these virtual libraries can be screened first in order to identify libraries for synthesis. 

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