The identification of depsipeptides by chemical ionisation mass spectroscopy

The chemical ionisation mass spectra of seven naturally occurring depsipeptides and some of their permethylated derivatives have been measured. The primary ionisation process involves an ester group and not an amide or other functionality. It probably occurs randomly when the molecule contains more than one ester link. Unlike electron impact mass spectra, those obtained under chemical ionisation conditions gave sequence information for all of the depsipeptides examined or their permethylated derivatives. A mechanism for the primary fragmentation is proposed.