Publication

Abstract : Fragmentation behavior of two classes of cyclodepsipeptides{,} isariins and isaridins{,} obtained from the fungus Isaria{,} was investigated in the presence of different metal ions using multistage tandem mass spectrometry (MSn) with collision induced dissociation (CID) and validated by NMR spectroscopy. During MSn process{,} both protonated and metal-cationized isariins generated product ions belonging to the identical {'}b-ion{'} series{,} exhibiting initial backbone cleavage explicitly at the [small beta]-ester bond. Fragmentation behavior for the protonated and metal-cationized acyclic methyl ester derivative of isariins was very similar. On the contrary{,} isaridins during fragmentation produced ions belonging to the {'}b{'} or/and the {'}y{'} ion series depending on the nature of interacting metal ions{,} due to initial backbone cleavages at the [small alpha]-ester linkage or/and at a specific amide linkage. Interestingly{,} independent of the nature of the interacting metal ions{,} the product ions formed from the acyclic methyl ester derivative of isaridins belonged only to the {'}y-type{'}. Complementary NMR data showed that{,} while all metal ions were located around the [small beta]-ester group of isariins{,} the metal ion interacting sites varied across the backbone for isaridins. Combined MS and NMR data suggest that the different behavior in sequence specific charge-driven fragmentation of isariins and isaridins is predetermined because of the constituent [small beta]-hydroxy acid residue in isariins and the cispeptide bond in isaridins.