Structural elucidation studies of polyketide tetrasubstituted δ-lactones by gas chromatography/tandem mass spectrometry and electrospray mass spectrometry

✍ Scribed by Kira J. Weissman; Gordon C. Kearney; Peter F. Leadlay; James Staunton

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 115 KB
• Volume: 13
• Category: Article
• ISSN: 0951-4198
• DOI: 10.1002/(sici)1097-0231(19991115)13:21<2103::aid-rcm760>3.0.co;2-y

✦ Synopsis

A series of tetrasubstituted polyketide delta-lactones were used to evaluate whether gas chromatography/tandem mass spectrometry (GC/MS/MS) and electrospray mass spectrometry (ESI-MS) are useful techniques for probing the structure and stereochemistry of such highly functionalised molecules. Analyses were performed with two commercially available mass spectrometers: a Finnigan/MAT GCQ instrument (CI source) and a Q-TOF Hybrid quadrupole time-of-flight instrument (ESI source). The analyses revealed that a range of variation in the structure and stereochemistry of the lactones did not affect the fragmentation pathway common to these molecules. By accurate mass determination (ESI-MS), the first two fragmentations were assigned to losses of water. Although it was anticipated that the initial dehydration would include the hydroxyl group at the 3-position of the lactones, evidence from deuterium- and (18)O-labelling studies suggests that the losses of water instead involve the oxygen atoms in the ester bond. Attempts to identify further the structures of daughter ions by GC/MS/MS were complicated by extensive rearrangements and non-specific hydrogen/deuterium migrations within the lactones. Together, these results illustrate the limitations of mass spectrometry in the structural elucidation of complex molecules. Copyright 1999 John Wiley & Sons, Ltd.