Structural Characterization of Cyclosporin A, C, and Microbial Bio-Transformed Cyclosporin A Analog AM6 Using HPLC–ESI–Ion Trap-Mass Spectrometry

In the 2014 study, researchers developed a method using high-performance liquid chromatography-electrospray ionization-ion trap mass spectrometry (HPLC-ESI-ion trap MS^n) to characterize the structures of cyclosporin A (CyA), cyclosporin C (CyC), and a bio-transformed CyA analog known as AM6. The method proved sensitive and accurate for detecting these compounds, with a recovery rate of CyA at 94 ± 3%, a detection limit of 2.5 ng/mL, and a quantification limit of approximately 5.3 ng/mL. The study also detailed the fragmentation patterns of CyA and CyC and identified structural differences between them. Additionally, the microbial bioconversion of CyA to AM6 by Streptomyces venezuelae was reported with a 40% conversion rate, and the structure of AM6 was characterized, marking the first time such identification was achieved using this analytical platform. The findings could facilitate the discovery of new cyclosporin analogs and improve the properties of existing ones.