Post-source decay analysis of dolastatin 10 and dolastatin 15 by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Dolastatin 10 and dolastatin 15 have been analyzed by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. Interestingly, in-source fragmentations could be easily detected for both compounds. Determination of the primary structure of both pseudopeptides could be done by using post-source decay (PSD) analysis. The molecular ion was used as the precursor ion in the case of dolastatin 10, whereas two in-source fragment ions and cationized (Na and K) precursors were selected in the case of dolastatin 15. An analogue of dolastatin 15 containing an amino alkyl linkage (compound 1) was also studied. Despite its close chemical structure its PSD spectrum exhibited a quite different pattern.