Electrospray ionization mass spectrometry as a valuable tool in the characterization of novel primaquine peptidomimetic derivatives

Mechanistic investigation of charge-remote and charge-driven fragmentation processes in 2,5-diphenyl-3,4-ethylenedioxythiophene diamidines

RATIONALE

Diphenylfuran diamidines represent an important class of DNA minor groove binders of high therapeutic interest as antitumor and antibacterial agents. This study aimed to investigate fragmentation patterns in mass spectra of four diamidine derivatives with significant antitumor activity, in order to gain more insight into the structures and stability of their putative biological metabolites.

METHODS

Compounds were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) using low-energy collision-induced dissociation (CID). Density functional theory calculations were performed to confirm the main fragmentation paths.

RESULTS

The most abundant ion present in mass spectra is the doubly protonated molecule, whereas singly protonated molecules are present to a lesser extent. In the simplest compound, 2,5-bis(4-amidinophenyl)-3,4-ethylenedioxythiophene, the main fragmentation path was loss of ammonia, followed by loss of HCN where possible. The fragmentation of the N-alkyl derivatives (N-isopropyl-, N-isobutyl-, N-cyclopentyl-) includes competition between loss of alkene and the corresponding amine, followed by loss of another alkene and formation of fragment ions present in the pathway of the parent compound.

CONCLUSIONS

The primary sites of fragmentations of investigated compounds are amidine groups, while breaking the core 3,4-ethylenedioxythiophene ring system does not take place. Fragmentation of the singly protonated molecule [M + H](+) occurs primarily on the charged side of the molecule, but a charge-remote process is energetically viable. The fragmentation mechanism of the alkyl derivatives revealed that singly and doubly protonated molecules cleave to the singly and doubly protonated molecules of the parent compound. Once formed, they are gradually transformed into nitrile. Copyright © 2016 John Wiley & Sons, Ltd.

Antiplasmodial drugs in the gas phase: a CID and DFT study of quinolon-4(1H)-imine derivatives

The gas-phase behavior of 12 quinolon-4(1H)-imine derivatives with antiplasmodial activity was investigated using electrospray ionization tandem mass spectrometry together with collision induced dissociation and density functional theory (DFT) calculations. The most probable protonation site was predicted by calculating the proton affinity (PA) values for each possible protonation site and it was found to be the imine nitrogen for all compounds under study. Fragmentation pathways of the protonated molecules were proposed and the assignment of product ion structures was performed taking into account theoretical calculations. The nature of the quinoline substituent was found to influence the gas-phase behavior of the compounds under study. The data acquired allowed to bracket the proton affinity of the quinolin-4-imine scaffold, which can be a useful starting point to choose appropriate references for determining PA values of this scaffold.

Schistosoma haematobium: identification of new estrogenic molecules with estradiol antagonistic activity and ability to inactivate estrogen receptor in mammalian cells

We have previously identified the expression of an estradiol (E2)-related molecule by Schistosoma haematobium total antigen (Sh). We now show that this molecule has an antagonistic effect of estradiol in vitro. Our results are consistent with the existence of an estrogenic molecule that antagonizes the activity of estradiol. We found evidence for this molecule as we identified and characterized by mass spectrometry new estrogenic molecules previously unknown, present in schistosome worm extracts and sera of Schistosoma-infected individuals. We also show that Sh is able to interact in vitro with estrogen receptor (ER), explaining how host endocrine system can favor the establishment of schistosomes. These findings highlight the exploitation of the host endocrine system by schistosomes and represent an additional regulatory component of schistosome development that defines a novel paradigm enabling host-parasite interactions. The identification of these molecules opens new ways for the development of alternative drugs to treat schistosomiasis.