Background. The emergence and dissemination of multi drug resistant (MDR) Gram-negative pathogens resistant to all available antibiotics poses a significant threat in clinical therapy. Among them, Klebsiella Pneumoniae clinical isolates overexpressing KPC-2 carbapenemase are the most worrisome, extending bacterial resistance to last resort carbapenems. [1-2] Materials/methods. Four boronic acid derivatives were designed and tested in vitro vs KPC-2.[3] In biological assays their ability to synergize last generation antibiotics was evaluated. X-ray crystallography was applied to confirm binding orientation and new compounds ability to reach consensus-binding sites in carbapenemases (Figure 1). Results. For the most actives active compounds nanomolar affinity was achieved. The best inhibitor has nanomolar affinity for the enzyme, a ligand efficiency of 0.78 kcal mol–1 and a molecular weight of 158 Da validating it as lead-like molecule. In biological assays against Escherichia coli overexpressing KPC-2 new derivatives restored susceptibility to cefotaxime, aztreonam and last resort carbapenems. Two crystallographic binary complexes of the best inhibitors binding KPC-2 were obtained at high resolution. Conclusion. We investigate the molecular recognition requirements in KPC-2 active site by boronic acid derivatives. Kinetic descriptions of slow binding, time dependent inhibition and interactions geometries in KPC-2 were fully investigated. This study will guide further lead optimization and development of more effective KPC-2 inhibitors. Figure 1 References [1] Jean-Marie Frère, Eric Sauvage and Frédéric Kerff. “From “An enzyme able to destroy penicillin » to carbapenemases: 70 years of beta-lactamase misbehavior” Current Drug Targets, (2016). Volume 16. (E-pub ahead of print). [2] Tondi, D.; Cross, S.; Venturelli, A.; Costi, MP; Cruciani, G.; Spyrakis, F. Current Drug Targets 2016 17, no. 9 (2016) [3] Tondi,D.; Venturelli,A.; Bonnet,R.; Pozzi, C.; Shoichet, BK.; Costi, M.P. JMC. 2014. 57 (12), pp 5449–5458.