title: Characterization of N-Boc/Fmoc/Z-N'-formyl-gem-diaminoalkyl derivatives using electrospray ionization multi-stage mass spectrometry.
abstract: N-Boc/Fmoc/Z-N'-formyl-gem-diaminoalkyl derivatives, intermediates particularly useful in the synthesis of partially modified retro-inverso peptides, have been characterized by both positive and negative ion electrospray ionization (ESI) ion-trap multi-stage mass spectrometry (MS(n)). The MS(2) collision induced dissociation (CID) spectra of the sodium adduct of the formamides derived from the corresponding N-Fmoc/Z-amino acids, dipeptide and tripeptide acids show the [M + Na-NH2CHO](+) ion, arising from the loss of formamide, as the base peak. Differently, the MS(2) CID spectra of [M + Na](+) ion of all the N-Boc derivatives yield the abundant [M + Na-C4H8](+) and [M + Na-Boc + H](+) ions because of the loss of isobutylene and CO2 from the Boc protecting function. Useful information on the type of amino acids and their sequence in the N-protected dipeptidyl and tripeptidyl-N'-formamides is provided by MS(2) and subsequent MS(n) experiments on the respective precursor ions. The negative ion ESI mass spectra of these oligomers show, in addition to [M-H](-), [M + HCOO](-) and [M + Cl](-) ions, the presence of in-source CID fragment ions deriving from the involvement of the N-protecting group. Furthermore, MS(n) spectra of [M + Cl](-) ion of N-protected dipeptide and tripeptide derivatives show characteristic fragmentations that are useful for determining the nature of the C-terminal gem-diamino residue. The present paper represents an initial attempt to study the ESI-MS behavior of these important intermediates and lays the groundwork for structural-based studies on more complex partially modified retro-inverso peptides.
authors.affiliation: Dipartimento di Chimica, Fisica e Ambiente, Università di Udine, Via del Cotonificio 108, I-33100, Udine, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Verardo
authors.forename: Andrea
authors.initials: A
authors.lastname: Gorassini
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D003959:Diamines / Q000737:chemistry*; D005449:Fluorenes / Q000737:chemistry*; D010455:Peptides / Q000032:analysis* / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D000596:Amino Acids; D003959:Diamines; D005449:Fluorenes; C016456:N(alpha)-fluorenylmethyloxycarbonylamino acids; D010455:Peptides
keywords: N-protected-N′-formyl-gem-diaminoalkyl derivatives; electrospray ionization; fragmentation; multi-stage mass spectrometry; structural elucidation