Electron-impact mass spectra EIMS of peptide derivatives

1 Electron-impact mass spectra (EIMS) of peptide derivatives 

Peaks expected in the electron impact mass spectrum (as expected on the basis of fragmentation each side of every CO) 

Peaks seen in the mass spectrum, due to loss of H20 from ions 18 mass units larger than 278 and 337 (favoured by glycine, and aromatic and heteroaromatic amino acids) 

Loss of propene (CH3-CH=CH2, mass 42) from the parent ion of valine-containing peptides (McLafferty rearrangement) 

Dolastatin 15 Mass-spectrometric analysis is well-suited to the study of samples that are accessible in microscopic quantities only. An example of this type, which was solved by MS, is Dolastatin 15, from the Indian Ocean sea hare Dolabella auric-ularia). It is a strongly cytostatic depsipeptide and therefore of considerable interest in leukaemia therapy (Pettit et al., 1989). Routine identification of its hydrolysis products showed that it must be the ester analogue of a heptapeptide with one ester bond in place of one amide bond. 

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