Synthesis of Pyrrolidine-fused β-lactams as Potential β-lactamase Inhibitors

A synthetic protocol for the preparation of novel 3,4-pyrrolidine-fused β-lactams was developed. The proposed 2,6-diazabicyclo[3.2.0]heptan-7-one scaffolds were constructed through an amido group-induced, potassium tert-butoxide-promoted intramolecular ring closure of 3-acylamino-4-oxiranyl-β-lactams as the key reaction step. Alternatively, the desired cyclization was also effected by means of a scandium triflate-mediated catalytic approach. In this way, a set of stereodefined 3,4-pyrrolidine-fused β-lactams was synthesized, which were preliminary evaluated as β-lactamase inhibitors. These first-line biological assessments led to the identification of a 2-benzoyl-6-(4-methoxyphenyl)-substituted diazabicyclo structure as an eligible starting point for further β-lactamase inhibitor optimization studies.