Study Of Proton Or Alkali Induced Fragmentation Mechanism Of A Series Of Tetracycline Compounds By MS

Since the invention of electrospray ionization source,mass spectrometry has widely been used in the pharmaceutical industry area.Electrospray ionization technology is a very soft ionization method,it could be used to differentiate chemical structures with subtle difference.Mostly,tandem mass spectrometry technology was used frequently to study the fragmentation pathways,gas phase reaction mechanism,isomer differentiation and impurity profiling.Tetracyclines are a family of board-spectrum antibiotics,Because of the absence of major adverse side effects,they are used widely.Represented by tigecycline,a new group of tetracyclines,named glycyclines,came to use recently.Sodium cromoglicate is a commonly used mastcell stabilizing drug,used for the treatment of asthma and a prophylactic drug for some other diseases.In the thesis,based on the fragmentation pathways of tetracyclines and sodium cromoglicate,the configuration and chemical structures of diastereomers and other impurities were proposed.In detail,following studies were conducted:1.The configuration of 4 pairs of tetracyclines and 4-epimers were studied.Oxytetracycline and 4-epimer showed diastereomer recognition.4-epimer had similar abundant fragment ion at m/z 444([M+H-NH3]+)and m/z 443([M+H-H2O]+),while m/z 444([M+H-NH3]+)was negligible for oxytetracycline.Theoretical calibration evidence showed,as tetracycline and 4-epimer twisted their rings,both of them formed intramolecular hydrogen bond,which resulted in the absence of [M+H-NH3]+ ion.Doxycline and chlorotetracycline showed little difference.2.Alkali metals adduct tetracyclines and respective 4-epimers were studied,all 4 pairs of sodium adduct species showed difference.Tetracyclines showed more tendency to form [M+Na-NH3]+ ions while 4-epimers were more likely to form [M+Na-NH3-H2O]+ ions.Lithium adducts oxytetracycline,tetracycline and chlorotetracycline showed apparent difference,while doxycycline showed little difference.Study shows it might be caused by the diameter of the ions,which resulted in difference for binding sites.Consequently,it twisted the configuration in different ways.As a result,their fragmentation showed difference.3.Based on the fragmentation mechanism of tetracyclines,chemical structure and configuration of minocycline 4-epimer and other 2 impurities were predicted.Meanwhile,HPLC-MS compatible separation method was also developed.4.An MS compatible HPLC method was developed for sodium cromoglycate.Based on the fragmentation mechanism,synthesis route and degradation pathways,chemical structures of 2 unknown impurities and 6 degradation products were all proposed.The research results provide researchers a unique route to study the fragmentation mechanism of tetracyclines.It also provides a rapid and effective method to speculate the chemical structures of impurities and absolute configuration of diastereomers.