Isolation and structural characterization of eight impurities in aztreonam

To comply with regulatory requirements, it is necessary to detect and separate the impurities generated during aztreonam synthesis or storage. The chromatogram of aztreonam revealed eight major impurities, which were purified through medium-pressure reversed-phase column and preparative High Performance Liquid Chromatography (HPLC). Through high resolution electrospray ionization mass spectroscopy (HRESIMS), as well as one- and two-dimensional nuclear magnetic resonance (NMR), their structures were confirmed as aztreonam acetate (Ⅰ), desulfated aztreonam (Ⅱ), anti-aztreonam (Ⅲ), open-ring aztreonam (Ⅳ), open-ring desulfated aztreonam (Ⅴ), open-ring desulfated aztreonam ethyl ester (VI), cis-deamino open-ring desulfated aztreonam (VII), and trans-deamino open-ring desulfated aztreonam (Ⅷ). Their exact concentrations were determined through quantitative nuclear magnetic resonance (qNMR) technique. Structural elucidation of the eight impurities through ¹H NMR, ¹³C NMR, the ¹H-¹H COSY, NOESY, HSQC, HMBC NMR and MS spectra was conducted. Especially, ⅥI and Ⅷ were identified as undescribed impurities here.