Structure elucidation of new kinds of bacitracin sulfonic acid based on high performance liquid chromatography-quadrupole time of flight-tandem mass spectrometry

Bacitracin is a mixture of antimicrobial peptides. Although the structures of bacitracins have been fully studied, the structure elucidation of the oxidation products of bacitracin has rarely been reported. In the present work, the bacitracin was treated by hydrogen peroxide solution to form bacitracin sulfonic acids (SO3H) directly, and the structures of bacitracin-SO3Hs were studied by high performance liquid chromatography-quadrupole time of flight-tandem mass spectrometry (HPLC-QTOF-MS/MS). It was demonstrated that the components of bacitracin, such as bacitracin A, B, and C could be site-specifically transformed to the corresponding oxidized product containing the SO3H group. The structure characterization of the oxidized products was elucidated based on the accurate molecular mass and the product ions obtained by MS/MS. Some new kinds of bacitracin J-SO3H, vinyl-bacitracin A-SO3H, bacitracin Y–SO3H and deamino-bacitracin Y–SO3H were identified. Furthermore, we also investigated the novel fragmentation behavior of the oxidized products. This is the first report to propose a neutral loss mechanism of SO3 that explains the characteristic ions of the vinyl-bacitracin A-SO3H and bacitracin Y–SO3H. Based on the structure analysis of the oxidation products of bacitracin, three transformation routes of bacitracin-SO3H generated from bacitracin were hypothesized and systematically summarized for the first time.