Fig. 4.

A previously described PqsR antagonist (45) featured a quinazolinone scaffold with a 7-chloro substituted ring. Removal of the chlorine atom led to a 10-fold drop in activity, whilst a 6-chlorine substituted ring was inactive. By contrast, the compound series described in this article found 6-chlorine substitution to be optimal. Both 45 and an endogenous ligand, NHQ (46) were successfully crystallised in the PqsR ligand-binding domain [32].