Negative ion electrospray ionization, fast-atom bombardment, and low energy tandem mass spectrometry were used for the analysis of dihydroxy-eicosatrienoic acids, which contain a vicinol diol and three nonconjugated double bonds, dihydroxy-eicosatetraenoic acids, which contain a conjugated triene structure, and trihydroxy-eicosatetraenoic acids, which contain a vicinol diol and a conjugated tetraene structure. In general, the product ion spectra were qualitatively similar for both modes of ionization, but electrospray ionization was strikingly more efficient in generation of abundant carboxylate anions that could be collisionally activated to yield product ion spectra. Collision-induced dissociation fragmentation mechanisms were described generally by α-hydroxy fragmentations directed by relative positions of double bonds and were consistent with stable isotope labeling studies. Rearrangement of the conjugated triene system in dihydroxy-eicosatetraenoic acids may be described by formation of a cyclohexadiene structure. Fragmentations that involve a two-proton transfer were described best by intramolecular oxidation of a hydroxy substituent to an enolate that resulted in an extended conjugated system. Collision-induced dissociation spectra obtained for the polyhydroxy unsaturated fatty acids, which are isobaric within each class, were uniquely descriptive of individual structures.

The low-energy collision-induced dissociation (CID) of the carboxylate anions generated by fast atom bombardment ionization of monohydroxy unsaturated fatty acids derived from oleic, linoleic, linolenic and arachidonic acids were studied in a tandem quadrupole mass spectrometer. The collisional activation spectra revealed structurally informative ions as to the position of the hydroxyl substituent in relationship to the sites of unsaturation. Five mechanisms are proposed for the fragmentation of hydroxyl substituted unsaturated fatty acids and are dependent upon the presence of alpha- or beta-unsaturation sites. These mechanisms include charge-remote allylic fragmentation, charge-remote vinylic fragmentation, charge-driven allylic fragmentation, charge-driven vinylic fragmentation, and homolytic fragmentation by an oxy-Cope rearrangement process. The assignment of specific fragmentation pathways was supported in many instances with deuterium-labeled analogs. Although no single fragmentation mechanism appears to predominate, a rational approach to the interpretation of these CID spectra is proposed. The CID spectra of unknown compounds could be used to establish the hydroxyl substituent position in relationship to certain sites of unsaturation but would not be indicative of all double bond locations. The oxy-Cope rearrangement is specific for a structural unit, namely the 3-hydroxy-1,5-diene moiety.

Background and purpose: Drug-induced prolongation of the QT interval can lead to torsade de pointes, a life-threatening ventricular arrhythmia. Finding appropriate assays from among the plethora of options available to predict reliably this serious adverse effect in humans remains a challenging issue for the discovery and development of drugs. The purpose of the present study was to develop and verify a reliable and relatively simple approach for assessing, during preclinical development, the propensity of drugs to prolong the QT interval in humans. Experimental approach: Sixteen marketed drugs from various pharmacological classes with a known incidence-or lack thereof-of QT prolongation in humans were examined in hERG (human ether a-go-go-related gene) patch-clamp assay and an anaesthetized guinea-pig assay for QT prolongation using specific protocols. Drug concentrations in perfusates from hERG assays and plasma samples from guinea-pigs were determined using liquid chromatography-mass spectrometry. Key results: Various pharmacological agents that inhibit hERG currents prolong the QT interval in anaesthetized guinea-pigs in a manner similar to that seen in humans and at comparable drug exposures. Several compounds not associated with QT prolongation in humans failed to prolong the QT interval in this model. Conclusions and implications: Analysis of hERG inhibitory potency in conjunction with drug exposures and QT interval measurements in anaesthetized guinea-pigs can reliably predict, during preclinical drug development, the risk of human QT prolongation. A strategy is proposed for mitigating the risk of QT prolongation of new chemical entities during early lead optimization.

GSK812397 is a potent entry inhibitor of X4-tropic strains of HIV-1, as demonstrated in multiple in vitro