Primary screening studies initially generate a list of compounds with the required biological activities (‘Hits’). These Hits rarely fulfil all the criteria for a quality “tool” compound as they typically show only a moderate affinity for the target and restricted selectivity.

To become a useful tool compound, the chemical properties of the initial Hits must therefore be iteratively improved by suitable structural modification. The post-screening Hit-to-tool optimisation process is carried out by accredited chemistry partner sites in GR-OPENSCREEN Members and is organised as a research collaboration between the assay provider and the respective chemistry site.