Targeting the RelSeq Synthetase Domain with Amino Benzoic Acid Centred Inhibitors

It is well established that antibiotic resistant bacteria have the genetics to specifically target and disarm an antibiotic’s mode of action. The more obscure phenotypic resistance, i.e. temporarily antibiotic tolerant, has yet remained relatively unexplored. These elusive sub-populations called persisters, are in a transient pseudoreduced metabolic state, sometimes occurring without environmental pressure. They can be multidrug tolerant and often contribute to chronic and recurring infections. Furthermore, persisters have been credited as an evolutionary stepping stone to antibiotic resistance. The downregulation of metabolism displayed by persisters is interconnected with activation of the stringent response and thus is believed to also be initiated by the accumulation of the intracellular signalling alarmone, guanosine penta- or tetra-phosphate, (p)ppGpp. The intracellular concentration of (p)ppGpp is controlled by the superfamily of RSH (RelA/ SpoT Homologue) proteins (Fig.1), making them potential targets for drug development to reduce chronic infections and help restrict antibiotic resistance. The main objective of this study is to design small molecules to selectively inhibit the synthetase domain of Rel proteins, from which we have chosen RelSeq (S. equisimilis) as our model protein. Among the chemotypes identified through in silico screening, we present the growth of the amino benzoic acid fragment into the first family of synthetase selective Rel inhibitors.