Identification by LC/MS(n) of degradates of a novel carbapenem antibiotic in an aqueous matrix.

Increased drug resistance in Staphylcocci and Enterococci to currently available antibiotics has significantly limited therapeutic options. Recently, a novel carbapenem antibiotic (Compound A) with a releasable side chain adjacent to the carbapenem was investigated to combat methicillin- and vancomycin-resistant Staphylococci and vancomycin-resistant Enterococci. The major advantage of Compound A over existing antibiotics can be attributed to the fact that cleavage of the side chain upon beta-lactam ring opening retained anti-bacterial activity while expelling the immunodominant epitope of the presumed beta-lactam hapten. In this work, LC/MS methods were developed to identify degradates of Compound A in an aqueous matrix utilized in assessing product safety and supporting analytical method and formulation development. A total of eight significant degradates were observed in this Compound A sample by LC/MS(n) and other techniques. Detailed structural analysis of degradates based upon LC/MS(n) data and other supporting results will be described in this work. Proposed molecular structures were confirmed by synthesis and use of authentic standards for several degradates. Degradates 1 and 4 were identified as degradates formed through the reversal of Michael reaction from Degradate 3 that is apparently formed by hydrolysis. Degradates 2 and 8 were found to be Hofmann elimination degradates. Degradates 5 and 6 are believed to be formed through dimerization of two parent molecules followed by the reversal of Michael reaction. Finally, Degradate 7 is attributed to a displacement reaction. Potential degradation pathways based upon these preliminary studies will also be discussed.