Structural characterization of glycoporphyrins by electrospray tandem mass spectrometry

Abstract

Porphyrin derivatives having a galactose or a bis(isopropylidene)galactose structural unit, linked by ester or ether bonds, were characterized by electrospray tandem mass spectrometry (ES-MS/MS). The electrospray mass spectra of these glycoporphyrins show the corresponding [M + H](+) ions. For the glycoporphyrins with pyridyl substituents and those having a tetrafluorophenyl spacer, the doubly charged ions [M + 2H](2+) were also observed in ES-MS with high relative abundance. The fragmentation of both [M + H](+) and [M + 2H](2+) ions exhibited common fragmentation pathways for porphyrins with the same sugar residue, independently of the porphyrin structural unit and type of linkage. ES-MS/MS of the [M + H](+) ions of the galactose-substituted porphyrins gave the fragment ions [M + H - C(2)H(4)O(2)](+), [M + H - C(3)H(6)O(3)](+), [M + H - C(4)H(8)O(4)](+) and [M + H - galactose residue](+). The fragmentation of the [M + 2H](2+) ions of the porphyrins with galactose shows the common doubly charged fragment ions [porphyrin + H](2+), [M + 2H - C(2)H(4)O(2)](2+), [M + 2H - C(4)H(8)O(4)](2+), [M + 2H - galactose residue](2+) and the singly charged fragment ions [M + H - C(3)H(6)O(3)](+) and [M + H - galactose residue](+). The fragmentation of the [M + H](+) ions of glycoporphyrins with a protected galactosyl residue leads mainly to the ions [M + H - CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2) - CO](+), [M + H - C(10)H(16)O(4)](+) and [M + H - protected galactose](+). The doubly charged ions [M + 2H](2+) fragment to give the doubly charged ions [porphyrin + H](2+) and the singly charged ions [M + H - protected galactose residue](+) and [M + H - CO(CH(3))(2)](+). For the porphyrins where the sugar structural unit is linked by an ester bond, [M + 2H](2+), ES-MS/MS showed a major and typical fragmentation corresponding to combined loss of a sugar structural unit and further loss of water, leading to the ion [M + 2H - sugar residue - H(2)O](2+), independently of the structure of the sugar structural unit. These results show that ES-MS/MS can be a powerful tool for the characterization of the sugar structural unit of glycoporphyrins, without the need for chemical hydrolysis.

Observation of phenyl-fused porphyrinoids during the ESI mass spectrometric analysis of meso-pentafluorophenyl-substituted porphyrin and corrole

“…The loss of a second phenyl group (expected m/z of 461.2) is of relatively low abundance. In general, these findings have been amply described before and serve here simply as benchmark data against which we evaluate the behavior of the pentafluorophenyl-derived analog [25,29,32].…”

“…Electrospray ionization (ESI) mass spectrometry (MS) is becoming a popular technique for the analyses of porphyrins [25][26][27][28][29][30][31][32][33][34][35].…”

Chemical Synthesis and Medicinal Applications of Glycoporphyrins

“…All porphyrin derivatives were tested against HSV-1 and HSV-2 in Vero cells. These compounds also proved to be suitable materials for detailed electrospray tandem mass spectrometry [227,228] . Similar concepts can also be employed to prepare unsymmetrical cationic glycoporphyrins.…”

Synthesis and differentiation of α‐ and β‐glycoporphyrin stereoisomers by electrospray tandem mass spectrometry

“…Interestingly, cross-ring fragmentations at sugar units showed high relative abundances in the MS/ MS spectra of the non-methylated derivatives studied previously. 27 This dissimilar behavior in these porphyrinic derivatives may be attributed to the charge preferential location in the porphyrin ring, linked to the inner nitrogens, rather than in the sugars unit as it was observed in the carbohydrate derivatives. 32 Analyzing the MS/MS spectra of both stereoisomers 1a and 1b it is possible to find differences.…”

“…25 More recently, ESI-MS/MS has already proved to be useful for the structural characterization of neutral and cationic tetra-aryl glycoporphyrins. 22,[26][27][28][29] Moreover, a study by MS/MS can also be an excellent and valuable tool to assess structural modification or degradation of photosensitizers that can occur during the in vitro process or in vivo cellular metabolisms.…”