International Journal of Mass Spectrometry 343–344 (2013) 1–8 Contents lists available at SciVerse ScienceDirect International Journal of Mass Spectrometry j ourna l ho me page: www.elsevier.com/locate/ijms Gas phase reactions of -substituted hetero-Diels–Alder adducts of meso-tetraphenylporphyrin using tandem mass spectrometry José C.J.M.D.S. Menezes a , M. Grac ¸ a P.M.S. Neves a,∗ , José A.S. Cavaleiro a , Cristina Barros a , Sérgio M. Santos b , Fernando de C. da Silva c , Vitor F. Ferreira c , M. Rosário M. Domingues a,∗ a Department of Chemistry and UI-QOPNA, University of Aveiro, 3810-193 Aveiro, Portugal b Department of Chemistry and CICECO, University of Aveiro, 3810-193 Aveiro, Portugal c Departamento de Química Orgânica, Universidade Federal Fluminense, 24020-141 Niterói, Rio de Janeiro, Brazil a r t i c l e i n f o Article history: Received 27 August 2012 Received in revised form 20 March 2013 Accepted 20 March 2013 Available online 28 March 2013 Keywords: Porphyrin Chromene Coumarin Benzopyran Retro-hetero-Diels–Alder Electrospray ionization mass spectrometry Tandem mass spectrometry a b s t r a c t -Substitued-meso-tetraphenylporphyrins with 5,10-dioxobenzo[g]- or 5,6-dioxobenzo[h]chromene, pyrano[3,2-c]coumarin and benzopyran moieties and the corresponding Zn(II), Cu(II) and Ni(II) com- plexes were studied by electrospray mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). These heterocyclic moieties have well established pharmacological activities and as such the introduction of these motifs into the -pyrrolic position of the porphyrin macrocycle can alter the prop- erties of the macrocycle and can produce new molecules with dual functions. The free base and Zn(II) complexes showed, in the ESI-MS spectra, the [M+H] + ions while the Cu(II) and Ni(II) complexes showed the M +• ions. The [M+H] + and M +• ions were induced to fragment and the corresponding ESI tandem mass spectra (MS/MS) were analyzed. The main fragmentation mechanism occurs in general via the retro hetero-Diels–Alder pathway while unexpected fragmentations or rearrangements were observed principally with the Zn(II) complexes. The analysis of the fragmentation pattern of all complexes indi- cates that the presence or absence of the carbonyl function in the -substituent led to the formation of secondary fragments. The differentiation of the isomers 2a and 2b was only possible by comparison of their MS/MS spectra. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Porphyrins have demonstrated promising applications in var- ious scientific fields such as catalysis, supramolecular chemistry, new electronic materials, sensors and drugs [1,2]. In medicine, for- mulations based on this type of derivatives are being applied in diagnosis of neoplastic diseases and in the photodynamic therapy of cancer and other diseases like the treatment of age-related macular degeneration, and in the inactivation of microbial pathogens. Their special role as photosensitizers in photodynamic therapy (PDT) and other applications require compounds with adequate structural features [3,4]. As part of our work on the synthesis and modification of meso-tetraarylporphyrins at the -pyrrolic position [5], we have synthesized a series of porphyrin derivatives incorporating the heterocyclic rings like 5,10-dioxobenzo[g]chromene, 5,6- dioxobenzo[h]chromene, pyrano[3,2-c]coumarin and benzopyran ∗ Corresponding authors. Tel.: +351 234 370 710/234 401 505; fax: +351 234 370 084. E-mail addresses: gneves@ua.pt (M.G.P.M.S. Neves), mrd@ua.pt (M.R.M. Domingues). via hetero-Diels–Alder reaction of -vinyl-meso-tetraphenyl- porphyrinatozinc(II) with adequate o-quinone methides (Fig. 1) [6]. These heterocyclic motifs are found in many natural products and are associated with antitumor activity, the treatment of Chagas dis- ease, molluscicidal, K ATP channel opening and myocardial ischemia activities [7–10]. The coupling of these entities containing well established pharmacological activities with porphyrins can lead to new molecules with dual function potentialities and possible applications in medicine. Preliminary studies have shown that the free bases 1 are able to generate singlet oxygen [11] which is crucial for their application as photosensitizers in PDT [1] or aPDI (antimicrobial photodynamic inactivation) [2]. Knowing that mass spectrome- try techniques can give significant structural information about porphyrinic derivatives [12,13] and to assess structural modifica- tion or degradation of photosensitizers that can occur during the in vivo cellular metabolism [14] we decided to study the gas-phase behavior of these compounds under electrospray mass spectrome- try (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). MS/MS is recognized as a valuable tool for the rapid and sensitive analy- sis of porphyrins in mixtures and for structural characterization of porphyrinic derivatives, giving important information about peripheral substituents [15–17]. So, with the possible application 1387-3806/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijms.2013.03.017