title: Is the atmospheric pressure chemical ionisation and collisionally induced methanol loss from protonated dehydroamino acids a retrosynthetic process?
abstract: Unsaturated 5(4H)-oxazolones lead, by methanolysis, to the corresponding dehydroamino acid derivatives. Interestingly, under atmospheric pressure chemical ionisation (APCI) conditions, the latter give rise, aside from abundant [M+H](+) ions, to [MHbondCH(3)OH](+) species, formally corresponding to the protonated oxazolones employed for their synthesis. Retrosynthetic processes have often been described as energetically favoured decompositions of odd-electron molecular ions but never invoked in APCI-activated fragmentations. To investigate this possible retrosynthetic process, occurring also under collisional conditions, some experiments on the deuterated analogues have been undertaken. The breakdown curves of [M+H](+) of oxazolones and [MHbondCH(3)OH](+) of the dehydroamino acid derivatives are superimposable, proving their structural identity and giving experimental evidence of the occurrence of a real retrosynthetic process from even-electron protonated molecules.
authors.affiliation: CNR, Istituto per le Scienze e Tecnologie Molecolari, Corso Stati Uniti 4, 35100 Padova, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Tubaro
authors.forename: Maria Anna
authors.initials: MA
authors.lastname: Fedrigo
authors.forename: Carlos
authors.initials: C
authors.lastname: Cativiela
authors.forename: Ana Isabel
authors.initials: AI
authors.lastname: Jiménez
authors.forename: Pietro
authors.initials: P
authors.lastname: Traldi