Title:Structure Analysis of Unsaturated Polymyxin E Components Based on
High-Performance Liquid Chromatography - Quadrupole/ Time of Flight
Tandem Mass Spectrometry and Photochemical Reaction
Volume: 18
Issue: 10
Author(s): Hanzhi Zhang*, Jingdan Zhao, Zhenhua Tian and Hao Liu
Affiliation:
- Analytical Department, Abiochem Biotechnology Co., Ltd, Shanghai 200241, China
- Department of Antibiotics and
Microorganisms, Shanghai Institute for Food and Drug Control, Shanghai 201203, China
Keywords:
2’, 3’-dehydro PME; 2’, 3’-epoxy PME; 2’, 3’-dihydroxy PME, HPLC-Q/TOF-MS, photochemical reaction, antibiotic resistance.
Abstract:
Background: Polymyxin E (PME), a complex of cationic cyclic lipodecapeptides, is
used to treat multidrug-resistant gram-negative bacterial infections. Besides the main components
PME1 and PME2, polymyxin containing unsaturated fatty acyl (FA) group with lower contents
can hardly determine the structure without chromatographic preparations and NMR.
Introduction: The peptide sequences of PME components have been carried out based on highperformance
liquid chromatography-quadrupole / time-of-flight mass spectrometry (HPLCQ/
TOF-MS). However, the components with double bonds on the FA, such as 2’, 3’-dehydro
PME1, were difficult to be determined or easily misjudged by MS/MS. The transformation of such
unsaturated components to be epoxidized or di-hydroxylated components can promote the acquisition
of more fragment ions in the MS/MS to assist in judging the position of double bonds on FA.
Methods: In this paper, the PME mixtures were dissolved in an equal proportion of 20% ACN
aqueous solution and 2-acetylpyridine. The above PME solution was transferred to a quartz cuvette
and irradiated with the ultraviolet lamp at 254 nm for 8h. The dehydro PME components
were converted to epoxy PMEs and dihydroxy PMEs. A fragmentation pathway of epoxidized or
di-hydroxylated components based on Q/TOF-MS/MS was proposed for the first time.
Results: According to the characteristic ions of epoxidized components and di-hydroxylated components,
2’, 3’-epoxy PME1/E2 and 2’, 3’-dihydroxy PME1/E2 were confirmed. It can be inferred
that the double bond is located at the 2’, 3’-position of FA.
Conclusion: The structure of unsaturated PME components with double bonds on the FA is elucidated
by HPLC-Q/TOF-MS combined with photochemical reaction. This strategy applies to other
lipopeptides containing unsaturated FA chains.
