We developed a method to elucidate the complete structure of triacylglycerols by means of high-energy collisional activation tandem mass spectrometry (MS/MS). Both ESI- and FAB-produced [M + NH4]+ and [M + met.]+ ions (where met. = Li, Na, and Cs) of triacylglycerols undergo charge-remote and charge-driven fragmentations. We emphasize the study of fragment ions from ESI-produced [M + NH4]+ and [M + Na]+ ions and FAB-produced [M + Na]+ ions. ESI-produced [M + NH4]+ ions fragment to produce four types of ions, [M + NH4 - RnCOONH4]+, [RnCO + 128]+, [RnCO + 74]+, and RnCO+ ions, from which the carbon number and the degree of unsaturation of each acyl group are obtained. In addition, three series of ions are produced by charge-remote fragmentations (CRFs), and analysis of their patterns gives the position and the number of double bonds on the acyl groups. Information about the position of each acyl group on the glycerol backbone, however, is not provided by collisionally activated dissociation of [M + NH4]+ ions. On the other hand, ESI- and FAB-produced [M + Na]+ ions fragment to form eight types of ions (named A-J ions) that, like those produced by CRF, are highly structurally informative. The absence of certain series members also carries useful structural information. Interpretation of these patterns enables one to obtain the number of carbons, degrees of unsaturation, and location of double bonds, as well as the positions of acyl groups on the glycerol backbone.
Fast atom bombardment-produced [M + Na]+ ions of tristearoylglycerol and [M - H]- ions of stearic or nervonic acid undergo charge-remote fragmentations (CRFs) to produce one series of product ions reflecting CnH2n + 2, losses, whereas electrospray ionization-produced ions fragment to give two series of product ions reflecting CnH2n + 2 and CnH2n + 1 losses. These results and those from previous studies show that the mechanisms and energetics of CRFs are complex and unsettled. We demonstrate that several pathways are simultaneously involved in CRFs, and the preference for certain pathways (by CnH2n + 1 and CnH2n + 2 losses) is determined by the internal energy of the compound itself and the ionization and activation energies that are applied to it.
Selective deuterium substitution as a means of ameliorating clinically relevant pharmacokinetic drug interactions is demonstrated in this study. Carbon-deuterium bonds are more stable than corresponding carbon-hydrogen bonds. Using a precision deuteration platform, the two hydrogen atoms at the methylenedioxy carbon of paroxetine were substituted with deuterium. The new chemical entity, CTP-347, demonstrated similar selectivity for the serotonin receptor, as well as similar neurotransmitter uptake inhibition in an in vitro rat synaptosome model, as unmodified paroxetine. However, human liver microsomes cleared CTP-347 faster than paroxetine as a result of decreased inactivation of CYP2D6. In phase 1 studies, CTP-347 was metabolized more rapidly in humans and exhibited a lower pharmacokinetic accumulation index than paroxetine. These alterations in the metabolism profile resulted in significantly reduced drug-drug interactions between CTP-347 and two other CYP2D6-metabolized drugs: tamoxifen (in vitro) and dextromethorphan (in humans). Our results show that precision deuteration can improve the metabolism profiles of existing pharmacotherapies without affecting their intrinsic pharmacologies.
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