Fragment-Based Drug Discovery of Inhibitors of Phosphopantetheine Adenylyltransferase from Gram-Negative Bacteria

The
discovery and development of new antibiotics capable of curing
infections due to multidrug-resistant and pandrug-resistant Gram-negative
bacteria are a major challenge with fundamental importance to our
global healthcare system. Part of our broad program at Novartis to
address this urgent, unmet need includes the search for new agents
that inhibit novel bacterial targets. Here we report the discovery
and hit-to-lead optimization of new inhibitors of phosphopantetheine
adenylyltransferase (PPAT) from Gram-negative bacteria. Utilizing
a fragment-based screening approach, we discovered a number of unique
scaffolds capable of interacting with the pantetheine site of E. coli PPAT and inhibiting enzymatic activity, including
triazolopyrimidinone 6. Structure-based optimization
resulted in the identification of two lead compounds as selective,
small molecule inhibitors of bacterial PPAT: triazolopyrimidinone 53 and azabenzimidazole 54 efficiently inhibited E. coli and P. aeruginosa PPAT and displayed
modest cellular potency against the efflux-deficient E. coli ΔtolC mutant strain.