Identification of diastereomeric chlorophyll allomers by atmospheric pressure chemical ionisation liquid chromatography/tandem mass spectrometry.
Atmospheric pressure chemical ionisation liquid chromatography/mass spectrometry (APCI-LC/MS) has been used for identification of the epimers of hydroxy, methoxy and methoxylactone allomers of chlorophyll a (13(2)-HO-chl a, 13(2)-MeO-chl a and 15(1)-MeO-lact-chl a), the hydroxy allomer of bacteriochlorophyll a (13(2)-HO-bchl a) and the hydroxy and methoxylactone allomers of bacterioviridin a (13(2)-HO-bvir a and 15(1)-MeO-lact-bvir a). The APCI mass spectra show that facile fragmentations involve the methoxyl or hydroxyl groups at the C-13(2) or C-15(1) chiral centres. Losses involving the C-13(2) or C-15(1) hydroxyl or methoxyl groups occur more easily from the S-epimer than from the R-epimer due to the greater relief of the steric strain associated with interaction with the bulky C-17 substituent. The differences in mass spectrometric fragmentation can be used as a diagnostic tool for the assignment of the stereochemical configuration at the C-13(2) or C-15(1) chiral centres.
Walker
J Stuart
JS
Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
Jie
Chi
C
Keely
Brendan J
BJ
D001274:Atmospheric Pressure; D001426:Bacterial Proteins / Q000032:analysis / Q000737:chemistry; D001429:Bacteriochlorophylls; D002734:Chlorophyll / Q000032:analysis* / Q000737:chemistry*; D000077194:Chlorophyll A; D002853:Chromatography, Liquid; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods*; D015394:Molecular Structure; D013237:Stereoisomerism
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D002734:Chlorophyll; C002084:bacteriochlorophyll c; D000077194:Chlorophyll A