Laser desorption ionisation–time of flight mass spectrometry of the tolyporphins, bioactive metabolites from the cyanobacterium Tolypothrix nodosa

Introduction – The tolyporphins are metabolites isolated from the cyanobacterium Tolypothrix nodosa, comprising a porphyrin-like macrocycle with C-glycoside, hydroxide or acetate substituents. Previous studies of porphyrins by MALDI/LDI-TOF MS indicate that strong radical cations and anions are usually observed in the parent spectra with little fragmentation of the macrocycle. The spectra of the tolyporphins were obtained and trends in the series utilised to partially characterise two new analogues. Objective – To examine tolyporphins by LDI-TOF MS and utilise trends observed to partially characterise two new analogues. Methodology – The tolyporphins were analysed by LDI-TOF MS in positive and negative ion mode and by a post source decay method (LIFT) in positive ion mode. Tolyporphin A was also analysed by MALDI-TOF MS for comparison. Results were analysed and used to obtain structural information on two new analogues. Results and Discussion – The resulting spectra generally contained intense radical cations or anions, with little fragmentation of the macrocyclic core or the C-glycosides observed. These results are consistent with previous studies of porphyrins. Major fragment ions observed in LIFT spectra yielded key structural information. An inseparable mixture of two tolyporphins was also examined. Analysis of the LIFT spectrum of the parent ion resulted in the postulation of structures of these two new analogues. Conclusions – Tolyporphins yield LDI-TOF mass spectra somewhat analogous to those of porphyrins; furthermore, the substituents fragment in a characteristic manner permitting partial characterisation of the new analogues tolyporphins L and M by comparison of their LDI-TOF mass spectra with those of the known analogues