Separating Isomers, Conformers, and Analogues of Cyclosporin
using Differential Mobility Spectroscopy, Mass Spectrometry, and Hydrogen–Deuterium
Exchange
posted on 2020-08-06, 22:19authored byK. H.
Brian Lam, J. C. Yves Le Blanc, J. Larry Campbell
Cyclosporins are
an invaluable class of drug used to prevent the
rejection of transplanted tissue. While the most popular drug in this
group is cyclosporin A, several other analogues are available, including
some enantiomeric and structurally isomeric forms. Unfortunately,
the presence of such isomers can make the detection and identification
of these drugs by mass spectrometry (MS) alone quite challenging.
Here, we demonstrate the separation and analysis of six cyclosporin
analogues using liquid chromatography (LC) and differential mobility
spectroscopy (DMS) coupled to MS. Using DMS, we demonstrate the separation
of three isomers: CycA and CycH (cyclosporin H), which are enantiomers,
and isocyclosporin A (a structural isomer of CycA and CycH). For several
of the cyclosporins, we can separate different conformers for each
isomeric form. After DMS separation, tandem mass spectrometry (MS/MS)
analyses of the separated isomers also distinguish these isomeric
forms of cyclosporin. In addition, we have probed differences between
each isomer by using gas-phase hydrogen–deuterium exchange
(HDX) immediately after DMS separation, which reveals differences
in the levels of intramolecular hydrogen bonding between each of the
cyclosporins.