Detection of the iron complexes with hydrolysis products of
cephalexin and cefradine upon high‐performance liquid
chromatography/electrospray ionization mass spectrometry
Faculty of Chemistry, Adam Mickiewicz
University, Umultowska 89B, 61‐614 Poznań,
Institute of Chemistry and Technical
Electrochemistry, Poznań University of
Technology, Berdychowo 4, 60‐965 Poznań,
R. Frański, Adam Mickiewicz University,
Faculty of Chemistry, Umultowska 89B,
61‐614 Poznań, Poland.
Cephalosporins (e.g. cephalexin, cefradine) are a major group of widely used
β‐lactam antibiotics. Hydrolysis of the β‐lactam ring is an important reaction (often undesired)
which leads to deactivation of β‐lactams. To the best of our knowledge there is no electrospray
ionization mass spectrometry (ESI‐MS) data reported concerning the products of hydrolysis of
The hydrolysis of cephalexin and cefradine was performed in aqueous NaOH
solutions. After the process the solutions were analyzed by high‐performance liquid chromatography
(HPLC)/ESI‐MS. The elemental compositions of the ions discussed were confirmed by the
accurate mass measurements on a quadrupole time‐of‐flight (QTOF) mass spectrometer.
Unexpectedly, complexes between the hydrolysis products of cephalexin and
) and iron cation were detected upon HPLC/ESI‐MS analysis, namely
the ions [(CFL
, although iron was not added to the analyzed
solutions or to the mobile phase. These ions were found to be very stable in the gas phase.
The detection of the complexes between the hydrolysis products of cephalosporins
and iron may have a positive impact on the sensitivity and specificity of HPLC/ESI‐MS analyses
of the hydrolysis products of some cephalosporins.
Hydrolysis of the β‐lactam ring leads to deactivation of β‐lactam
antibiotics. It is well known that, in the laboratory, hydrolysis of a β‐lactam
ring can be performed in basic solution (the process begins by
nucleophilic attack of the hydroxyl anion on the carbonyl carbon atom
of the four‐membered β‐lactam ring). In living organisms or in the
environment, hydrolysis of the β‐lactam ring is an enzymatic process.
There are a number of enzymes (β‐lactamases) which effectively
deactivate the antibiotics.
Hydrolysis of the β‐lactam ring may be
also promoted by metal cations.
Because of the importance of
the process of hydrolysis of the β‐lactam ring this process has been
also theoretically studied in detail.
Awidelyusedmajorgroupofβ‐lactam antibiotics are cephalosporins,
e.g. cephalexin (CFL) and cefradine (CFR) (shown in Scheme 1).
Electrospray ionization mass spectrometry, usually coupled with
high‐performance liquid chromatography (HPLC/ESI‐MS), has been
successfully applied to their analysis.
However, there is little
nuclear magnetic resonance (NMR) data reported concerning the
products of their hydrolysis
and, to the best of our knowledge,
there is no ESI‐MS data reported concerning the products. It is
reasonable to expect that the products of cephalosporin hydrolysis
are unstable and undergo further transformation (e.g. to the
diketopiperazine conjugates) which may affect their detection. In
general, there is no ESI‐MS data reported concerning the products
of hydrolysis of cephalosporins (to the best of our knowledge).
Only in a paper by Chen et al. was it mentioned that the product
of cephalexin hydrolysis was identified by LC/MS.
A number of
cephalosporins have been subjected to hydrolysis and the products
have been analyzed by ESI‐MS.
However, the identified
products were degradation products and not hydrolysis products.
By strictly hydrolysis product we mean the compound which is
formed by addition of water to the β‐lactam ring of the parent
antibiotic. As a consequence, the hydrolysis product does not have
Received: 18 November 2017 Revised: 12 January 2018 Accepted: 26 January 2018
576 Copyright © 2018 John Wiley & Sons, Ltd. Rapid Commun Mass Spectrom. 2018;32:576–582.wileyonlinelibrary.com/journal/rcm