The modification of beta-lactam antibiotics continues to be a promising means for the improvement of this very important class of antimicrobials. The varied useful attributes of the new oxacephalosporin moxalactam, namely broad spectrum of activity, favorable pharmacokinetic profile, and stability, prompts us to propose the synthesis and evaluation of a related oxacephalosporin structure. Recently we synthesized a novel tricyclic oxacephalosporin which is expected to lead to a series of compounds from which antimicrobial activity is expected. We now propose the synthesis of a series of these analogs and their evaluation against a broad spectrum of bacteria. Based upon preliminary structural analysis this new oxacephalosporin appears to be related closely to penicillins, and therefore we anticipate significant gram positive activity in addition to the gram negative activity cephalosporins generally possess. By analogy with moxalactam we anticipate resistance to bacterial enzymatic inactivation, an attribute which is increasingly important due to widespread resistance to current antibiotics. This Phase I program wiil provide the basis for the development of structures with improved antibacterial properties and will provide structure activity information in the new class of oxacephalosporins represented by moxalactam.