Mass spectrometric amino acid structure determination in ergopeptines

Collision-induced dissociation (CTD) mass spectra of selected diagnostic ions generated by electron ionization of a series of natural ergopeptines have been studied in order to develop a general protocol suitable for rapid identification of the possible amino acids present. CID spectra of ions comprising the complete peptide portion of an alkaloid provide information on the alkyl side chain size of the second and third amino acid and characterise the alkyl branching pattern of the third amino acid, Isobaric amino acids at the third position in ergopeptines can be distinguished unambiguously from the CID spectra of the corresponding immonium ions. Acylium-type ions representing the residue at the second position reveal information on the alkyl residue size only. The suggested general amino acid analysis protocol has been used for structural elucidation of the 9,10-dihydro derivative of a new ergot alkaloid, ergosedmine, a congener of ergocristine produced by Claviceps purpurea.