Tandem mass spectrometry analysis of synthetic opioid peptide analogs

Five synthetic opioid peptides that were designed to have specific opioid receptor-binding properties were studied by low energy collision-induced dissociation (CID) tandem mass spectrometry (MS/MS). The MS/MS data are required for the analysis of those peptides in ovine plasma in a study to determine the placental transfer of the peptide to the fetus. The synthetic enkephalin-related peptides were: Tyr-D-Arg-Phe-Lys-NH2, (DALDA), N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH, (ICI 174,864), Tyr-D-Thr-Gly-Phe-Leu-Thr, (DTLET), Tyr-D-Pen-Gly-Phe-D-Pen-OH, (DPDPE), and D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, (CTAP). Liquid secondary ion mass spectrometry (LSIMS) was used for sample desorption-ionization, and a hybrid (E1BE2qQ) tandem mass spectrometer was used to collect the product-ion spectra. A protonated molecule ion, [M + H]+, was observed for each peptide. Amino acid sequence-determining fragment ion were produced by CID and collected by MS/MS for the three linear peptides, and also for the two disulfide-bond-containing peptides in their unreduced and dithiothreitol (DTT)-reduced forms. The detection level for the [M + H]+ ion of DTLET was ca. 3 pmol; and the stabilities of the CTAP and ICI analogs in plasma were studied.