Fig. 7.

Proposed mechanisms of biapenem and tebipenem adduct formation and degradation. The figure shows the chemical steps (steps 1–10) to reach the crystallographically observed adducts from the expected initial (intact) carbapenem adduct of the enzyme. The expected mass differences in each step of the reaction are annotated for comparison with the observed species in the mass spectrometry experiments. A final decarboxylation step (step 11), where the product is observed in the ESI mass spectra but not in the crystal, is included as a possible explanation. The mass increases caused by the adducts were calculated using the program ChemDraw®(v 15.0.0.106; 1985-2015 PerkinElmer Informatics, Inc.)