Diastereomer recognition of three pairs of tetracyclines by electrospray ionization mass spectrometry

Abstract

Rationale Stereoisomer profiling is always a difficult issue. Based on the difference between diastereomers, usually because of steric hindrance, isomers can be differentiated by mass spectrometry (MS), although it is often not an easy task. In the current study, tetracycline, chlortetracycline and doxycycline could be distinguished from their respective 4‐epimers by MS. Methods The electrospray ionization tandem mass spectrometry (ESI‐MSn) analyses were carried out on a Bruker 3000plus ion trap mass spectrometer. For MS/MS experiments, the collision energy was set between 0.18 and 0.45 V to perform energy‐resolved mass spectrometry (ERMS). Test solutions were prepared in methanol/water (90:10, v/v) at a concentration of 10 μg/mL. Results Compared with the collision‐induced dissociation (CID) spectrum of protonated tetracycline, the most abundant peak changed from m/z 427 to m/z 410 for 4‐epitetracycline. For chlortetracycline and its 4‐epimer, differences in relative abundance were observed too. In the CID spectrum of a fragment ion of doxycycline, the abundance of m/z 154 was relatively higher than for the 4‐epimer, showing the same trend as in the CID spectra of the other two pairs of tetracyclines. Conclusions The CID spectra of tetracycline and chlortetracycline were different from those of their 4‐epimers. The CID spectra of protonated doxycycline and its 4‐epimer showed only a subtle difference, but the m/z 154 fragment ion in the CID spectra of the fragment ion at m/z 428 offers the possibility to differentiate both epimers.

Elevated Membrane Potential as a Tetracycline Resistance Mechanism in Escherichia coli

“…The protonation of tetracycline at different pH 6.6, pH 7.1, pH 7.4, pH 7.9, and pH 8.4 was analyzed by mass spectrometry. A 445 m / z peak was detected in every pH, which is tetracycline as a reference indicated . Besides it, tetracycline had a peak at 446 m / z at pH 6.6 and 7.1 and a peak at 467 m / z at pH 7.4, 7.9, and 8.4, indicating that tetracycline acquires a hydrogen ion and a sodium ion, respectively.…”

“…A 445 m/z peak was detected in every pH, which is tetracycline as a reference indicated. 31 Besides it, tetracycline had a peak at 446 m/z at pH 6.6 and 7.1 and a peak at 467 m/z at pH 7.4, 7.9, and 8.4, indicating that tetracycline acquires a hydrogen ion and a sodium ion, respectively. On the other hand, it is possible to confirm whether tetracycline protonation is pHdependent based on the effect of the relationship between the isoelectric point (PI) and pH on protonation.…”