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. Copyright © 2004 John Wiley & Sons, Ltd.