The Identification Of A Novel Impurity In Azithromycin And Intramolecular Oxygen Transfer Reactions Of Sulfonamides In ESI-MS~n

Drug safety assessment is highly related to human health.The unknown impurity in bulk drugs is one of the most important concerns of drug safety assessment.Impurity profiling methods mainly include on-line and off-line analysis,and the application of mass spectrometry is more or less involved in these analytical methods.As an important analytical technology,mass spectrometry is applied not only in compound characterization,but also in the investigation of gas-phase reactions.On the one hand,the study of gas-phase reaction lays a theoretical foundation for the application of mass spectrometry in analytical chemistry;on the other hand,it also provides useful help for the identification of unknown structure.In this dissertation,we identified a novel impurity in azithromycin bulk drug for the first time using multidimensional nuclear magnetic resonance technique,and we also investigated the intramolecular oxygen transfer reaction of sulfonamides in the gas phase through positive ion mode electrospray ionization tandem mass spectrometry(ESI-MSn)under collision induced dissociation.1.Isolation and structure identification of the impurity P in azithromycin bulk drug.This impurity was detected at a level of 17.2%through high performance liquid chromatography(HPLC).A certain amount of this impurity was then prepared through 50DAC preparative chromatography system under optimized separation conditions.Its chemical formula was determined to be C39H72N2O13 by high-resolution mass spectrometry.The functional groups in this impurity were identified through infrared spectroscopy and ultraviolet-visible spectroscopy.The chemical structure of this unknown was ultimately determined by multidimensional nuclear magnetic resonance analysis.Our results showed that this impurity is a new compound.2.Study on the intramolecular oxygen transfer in the gas-phase dissociation of protonated sulfonamides under ESI-MSn condition.Taking 4-aminobenzenesulfonamide as a model compound,we investigated the intramolecular oxygen transfer reaction in collision induced dissociation mode.It was found that the protonated 4-aminobenzenesulfonamide was converted to 4-aminobenzenesulfonyl cation through the loss of NH3 in the ESI-MS/MS.Subsequently,the oxygen atom of the sulfonyl group acted as a nucleophile to attack the carbon of the benzene ring to form a three-membered ring transient state(TS1),and with the loss of SO,TS1 was converted to the skeleton-rearranged final product,i.e,,4-aminophenyl-1-ylium.In the study of substituent effect,we found that the corresponding phenoxonium cations were not observed when the amino group on the para-position of the benzene ring was substituted for some chemical groups such as methyl group,due to the conjugation effect.The mechanism of this intramolecular oxygen transfer process was validated by means of deuterium labeling experiment,theoretical calculation and substituent effect study.