The word “REOS” and the concept was first described was introduced by researchers at Vertex. REOS (rapid elimination of swill) filter is based on more than 100 SMARTS strings collected from literature data describing non-druglike functionalities associated with promiscuous ligands and frequent hitters. Efficiency of lead optimization efforts can be significantly increased by eliminating these problematic compounds to focus on top quality drug candidates only.
If you are looking for drug candidates or even just suitable probe molecules to analyze a biological target, it is highly recommended to exclude molecules containing reactive functional groups as these can be frequently associated with toxicity and lack of selectivity. Conclusions drawn from biological experiments with compounds containing such functional groups might therefore be misleading. Unless you are looking for reagents for further synthesis or for building a combinatorial library, the REOS filter is highly recommended to filter out problematic compounds.
There are currently no options available for the REOS filter. We plan to make it customizable in future.
Molecules not containing any reactive functional groups defined in the SMARTS queries of the REOS filter