The 2-oxoazetidinylacetate sodium salt was synthesized as a model of a minimal P-lactam drug. This compound and the monobactam aztreonam were assayed as substrates of the Metallo-p-lactamase Bell. None of them was hydrolyzed by the enzyme. While the azetidinone was not able to bind Bell, aztreonam was shown to bind in a nonproductive mode. These results provide an explanation for the unability of Metallo-ß-lactamases to inactive monobactams and give some clues for inhibitor design. (c) 2007 Elsevier Ltd. All rights reserved.