High Performance Liquid Chromatography-Quadrupole/Time of Flight–Tandem Mass Spectrometry for the Characterization of Components in Bacitracin
2020
Qin, Feng | Zhang, Hanzhi | Liu, Hao | Zhang, Xiangmin
A selective method of high performance liquid chromateography-quadrupole/time of flight-tandem mass spectrometry is described for the characterization of related substances in bacitracin samples. The chromatographic separation of the components of bacitracin was carried out using a Diamonsil Plus C18 column, a mixture of ammonium formate buffer (50 mM, pH 4.0) and acetonitrile was used as mobile phase under gradient elution. Baseline separation of bacitracin B1 and B2 were resolved for the first time. A complete strategy for structure characterization based on the accurate molecular weight and the diagnostic fragment ions obtained by MS/MS was elucidated. Three fragmentation routes were summarized in detail from the ions of Q/TOF–MS with accurate mass values. It was worth mentioning that the characteristic ions of amino acid residues can help to determine the structure of the new components of bacitracin. About 33 components were detected and the sequences of known components like bacitracin A, B1/B2/B3, C1/C2/C3, H1/H2/H3 and F were confirmed. Bacitracin E, J1/J2/J3, isomers of the main components of bacitracin (A, B and C), dehydration product and degradation products were sequenced completely. A proposed mechanism explanation for the transformation of isomers of bacitracin A was also approached. The structure of a new and specific component (component 5) containing two methylene on the N-terminal isoleucine residue and one vinyl group on the thiazoline or one ethyl group on the thiazole was proposed and described.
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