Proposed fragmentation pathway of phenethylamine and tyramine alkaloids containing an imidazolium ring from S. aquimarina.

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... or C8H8O (120.0570 amu) diagnostic of PEA or TYM (Figures 4 and 5). Particularly, shewazoles having at least one TYM-derived motif display the [M+H-C8H8O] + ion as the most abundant fragment ( Figure 5C). ...

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... shewazoles having at least one TYM-derived motif display the [M+H-C8H8O] + ion as the most abundant fragment ( Figure 5C). The α fragmentation shown in Figure 4 is usually found in N-alkyl imidazoles and implies cleavage of the N-C bond with simultaneous proton transfer from the leaving styrene/hydroxystyrene moiety to the nitrogen [49]. In addition, the formation of the cognate δ ions, i.e., [C8H9] + and/or [C8H9O] + , occurs during fragmentation of shewazoles, thus confirming the presence of PEA and/or TYM, as already observed for shewamidines (Fig- ures 4 and 5). ...

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... α fragmentation shown in Figure 4 is usually found in N-alkyl imidazoles and implies cleavage of the N-C bond with simultaneous proton transfer from the leaving styrene/hydroxystyrene moiety to the nitrogen [49]. In addition, the formation of the cognate δ ions, i.e., [C8H9] + and/or [C8H9O] + , occurs during fragmentation of shewazoles, thus confirming the presence of PEA and/or TYM, as already observed for shewamidines (Fig- ures 4 and 5). Sequential losses of two styrene/hydroxystyrene molecules (C8H8/C8H8O) from the [M+H] + ions generate the ε fragment ion corresponding to the central imidazolium core (Figure 4, fragmentation α + ε), as shown for discolins [48]. ...

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... addition, the formation of the cognate δ ions, i.e., [C8H9] + and/or [C8H9O] + , occurs during fragmentation of shewazoles, thus confirming the presence of PEA and/or TYM, as already observed for shewamidines (Fig- ures 4 and 5). Sequential losses of two styrene/hydroxystyrene molecules (C8H8/C8H8O) from the [M+H] + ions generate the ε fragment ion corresponding to the central imidazolium core (Figure 4, fragmentation α + ε), as shown for discolins [48]. The presence of the imidazolium ring is also suggested by the homolytic scission reaction leading to formation of the radical cation ζ from the fragment ion α (Figures 4 and 5). ...

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... losses of two styrene/hydroxystyrene molecules (C8H8/C8H8O) from the [M+H] + ions generate the ε fragment ion corresponding to the central imidazolium core (Figure 4, fragmentation α + ε), as shown for discolins [48]. The presence of the imidazolium ring is also suggested by the homolytic scission reaction leading to formation of the radical cation ζ from the fragment ion α (Figures 4 and 5). ...

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... in-depth investigation of the MS tandem spectra allowed us to predict the substitution patterns of the central imidazolium scaffold as detailed in Table 3. As observed in discolins and substituted imidazoles [50], [M+H] + pseudomolecular ions of shewazoles showed RCN and/or HCN losses which were useful to establish the alkyl and phenyl substituents directly linked to the imidazolium ring (Figure 4, fragmentations β and γ). A putative pathway leading to fragments arising from RCN and/or HCN losses may involve the formation of an ion species stabilized by ring expansion with concomitant side chain migration. ...

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... putative pathway leading to fragments arising from RCN and/or HCN losses may involve the formation of an ion species stabilized by ring expansion with concomitant side chain migration. These fragmentation pathways were supposed to produce azirine cations as described in Figure 4 [51]. Notably, neutral loss of R1CN generates a more abundant ion as compared to R2CN and R3CN losses according to MS/MS spectra recorded for discolins [48]. ...

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... this observation was used to assign the position of the R1 substituent group. Moreover, the α-type fragment ions of shewazoles were shown to undergo RCN loss through a similar mechanism, thereby yielding the η-type azirine cations, which allowed for the identification and position assignment of the R1, R2, and R3 groups ( Figures 4 and 5). ...

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... the antiviral activity was investigated through all the previous four experiments described above. Once again, no inhibition was detected in cells pre-treatment and in post-infection assays ( Figure S4), while in the virus pre-treatment and co-treatment assays antiviral activity was very similar to that observed against HSV-1 ( Figure 14). Indeed, F2 showed 75% of viral inactivation in the co-treatment assay and complete inactivation in the virus pre-treatment assay at the highest concentration tested. ...

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... Materials: The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/pharmaceutics15082139/s1, Table S1: Diketopiperazines from Shewanella aquimarina, Figure S1: Neutral loss/precursor m/z plot from HR-MS/MS data of the F2 fraction; Figure S2: Biofilm degradation; Figure S3: Antiviral activity vs. HSV-1; Figure S4: Antiviral activity vs. HCoV-229E; Figure S5: Antiviral activity vs. PV-1, Figure S6: MRSA antibiogram, Figure S7: MSSA antibiogram, Figure S8: β-Lactamase antibiogram, Figure S9: QRSA antibiogram, Figure S10: MLSB antibiogram. ...