Collisional activation decomposition of actinomycins using tandem mass spectrometry

The collisional activation (xenon) decomposition of actinomycin V, dactinomycin, 7-nitrodactinomycin, 7-aminodactinomycin, and a mixture of dactinomycin, actinomycin C1 and actinomycin C2 was studied using a triple-quadrupole mass spectrometer with fast atom bombardment (xenon) ionization. Fragmentation pathways of the structurally significant ions were rationalized by assuming an initial McLafferty rearrangement at the ester linkage between the methylvaline and the threonine of both rings to form linear pentapeptides, followed by fragmentation in either pentapeptide yielding typical sequence ions and sequence cleavages from both rings.