Identifying the Related Compounds Using Electrospray Ionization Tandem Mass Spectrometry: Bromotyrosine Alkaloids from Marine Sponge Psammaplysilla Purpurea

Abstract

We have investigated extracts of marine sponge Psammaplysilla purpurea during three collections from Mandapam (Tamil Nadu, India) and Okha (Gujarat, India) and indentified two new bromotyrosine alkaloids, purpurealidin I (7) and J (8) using electrospray ionization tandem mass spectrometry (ESI-MS/MS). This sponge has tremendous chemical diversity of bromotyrosine alkaloids. Here we have used the proteomics approach in identifying related bromotyrosine alkaloids based on the predicated mass fragmentation pattern. The focus is on the examination of detailed product ion spectra of six known compounds that allowed identification of new compounds based on its mass fragmentation pattern. The isotopic pattern of the peaks for protonated molecules indicated the number of bromine atoms present in the molecule. During MS/MS studies, the most prominent product ion peak is for the presence of the side chain propane with either free NH2 or NHMe or NMe2. The cleavage at C–C bond between oxime–amide carbonyl and amide–phenoxy moiety also gave characteristic product ions. The ESI-MS spectra for all three collections show that the bromotyrosine metabolites vary during different seasons and also geographical location, although some common metabolites were observed during the three collections. Thus, ESI-MS/MS is a method of choice in identifying the related compounds.