Further exploration of the collision-induced dissociation of select beta blockers: Acebutolol, atenolol, bisoprolol, carteolol, and labetalol

Beta blockers are a class of drugs commonly used to treat heart-related diseases; they are also regulated under the World Anti-Doping Agency. Tandem mass spectrometry is often used in the pharmaceutical industry, clinical analysis laboratory, and antidoping laboratory for detection and characterization of drugs and their metabolites. A deeper chemical understanding of dissociation pathways may eventually lead to an improved ability to predict tandem mass spectra of compounds based strictly on their chemical structure (or vice versa), which is especially important for characterization of unknowns such as emerging designer drugs or novel metabolites. In addition to providing insights into dissociation pathways, the use of energy-resolved breakdown curves can produce improved selectivity and lend insights into optimal fragmentation conditions for liquid chromatography-tandem mass spectrometry LC-MS/MS workflows. Here, we perform energy-resolved collision cell and multistage ion trap collision-induced dissociation-mass spectrometry (CID-MS) experiments, along with complementary density functional theory calculations, on five beta blockers (acebutolol, atenolol, bisoprolol, carteolol, and labetalol), to better understand the details of the pathways giving rise to the observed MS/MS patterns. Results from this work are contextualized within previously reported literature on these compounds. New insights into the formation of the characteristic product ion m/z 116 and the pathway leading to characteristic loss of 77 u are highlighted. We also present comparisons of breakdown curves obtained via qToF, quadrupole ion trap, and in-source CID, allowing for differences between the data to be noted and providing a step toward allowing for improved selectivity of breakdown curves to be realized on simple instruments such as single quadrupoles or ion traps.

Microheterogeneity and Individual Differences of Human Urinary N-Glycome under Normal Physiological Conditions

Urine is considered an outstanding biological fluid for biomarker discovery, reflecting both systemic and urogenital physiology. However, analyzing the N-glycome in urine in detail has been challenging due to the low abundance of glycans attached to glycoproteins compared to free oligosaccharides. Therefore, this study aims to thoroughly analyze urinary N-glycome using LC-MS/MS. The N-glycans were released using hydrazine and labeled with 2-aminopyridine (PA), followed by anion-exchange fractionation before LC-MS/MS analysis. A total of 109 N-glycans were identified and quantified, of which 58 were identified and quantified repeatedly in at least 80% of samples and accounted for approximately 85% of the total urinary glycome signal. Interestingly, a comparison between urine and serum N-glycome revealed that approximately 50% of the urinary glycome could originate from the kidney and urinary tract, where they were exclusively identified in urine, while the remaining 50% were common in both. Additionally, a correlation was found between age/sex and the relative abundances of urinary N-glycome, with more age-related changes observed in women than men. The results of this study provide a reference for human urine N-glycome profiling and structural annotations.

Positional Assignment of C-C Double Bonds in Fatty Acyl Chains of Intact Arsenosugar Phospholipids Occurring in Seaweed Extracts by Epoxidation Reactions

Water-soluble diacyl arsenosugar phospholipids (As-PL) are natural products widespread in marine animals and algae, including the brown alga Undaria pinnatifida, also known as wakame. The systematic recognition of As-PL has been hampered by the lack of standard and of qualitative methods to establish the carbon-carbon double bond positions of unsaturated fatty acyl chains. Here, the epoxidation reaction of fatty acyl substituents of As-PL was carried out with high selectivity by meta-chloroperoxybenzoic acid and the C-C double bond localization was established by collision-induced dissociation of epoxidized species as deprotonated molecules, [epoM - H]-. Reversed-phase liquid chromatography (RPLC) separation and a sequential triple-stage MS (i.e., MS3) analysis of unsaturated and epoxidized As-PL were very helpful to characterize the carbon-carbon double bond locations of both sn-1 and sn-2 fatty acyl chains, starting from a diagnostic product ion pair with 16.0 Da mass difference. These results indicate that intact As-PL can be annotated in terms of fatty acyl chain composition and in terms of their C-C double bond position(s). Interestingly, hexadecenoic (16:1 Δ9) and octadecenoic (18:1 Δ9) along with octadecadienoic (18:2 Δ9,12) and octadecatrienoic (18:3 Δ9,12,15) were found to be the most abundant unsaturated fatty acyl chains of As-PL in the brown alga wakame, thus confirming it as a good source of essential fatty acids with a balanced ω6/ω3 ratio. Although the toxicity of As-including metabolites of algal As-PL is still a matter of debate and needs to be studied in more detail, the described approach can be exploited to assess if As-PL could contribute to the supply of essential fatty acids related to the use of algae as nutritious food.

Bioactive (Co)oligoesters as Potential Delivery Systems of p-Anisic Acid for Cosmetic Purposes

This article reports the studies on bioactive (co)oligoesters towards their use as controlled delivery systems of p-anisic acid. The objects of the study were oligo[3-hydroxy-3-(4-methoxybenzoyloxymethyl)propionate], (p-AA-CH₂-HP)_n oligoester, and oligo[(3-hydroxy-3-(4-methoxybenzoyloxymethyl)propionate)-co-(3-hydroxybutyrate)] [(p-AA-CH₂-HP)_x-co-(HB)_y (co)oligoesters containing p-anisic acid moiety (p-AA, as the bioactive end and side groups) connected to the polymer backbone through the susceptible to hydrolysis ester bonds. A thorough insight into the hydrolysis process of the bioactive (co)oligoesters studied has allowed us to determine the release profile of p-AA as well as to identify polymer carrier degradation products. The p-AA release profiles determined on the basis of high-performance liquid chromatography (HPLC) measurements showed that the release of the bioactive compound from the developed (co)oligoester systems was regular and no burst effect occurred. Biological studies demonstrated that studied (homo)- and (co)oligoesters were well tolerated by HaCaT cells because none of them showed notable cytotoxicity. They promoted keratinocyte growth at moderate concentrations. Bioactive (co)oligoesters containing p-anisic acid moiety had somewhat decreased cell proliferation at the highest concentration (100 µg/mL). The important practical inference of the current study is that the (co)oligoesters developed have a relatively large load of the biologically active substance (p-AA) per polymer macromolecule, which unlocks their potential application in the cosmetic industry.

Electrospray multistage mass spectrometry in the negative ion mode for the unambiguous molecular and structural characterization of acidic hydrolysates from 4-O-methylglucuronoxylan generated by endoxylanases

A rapid analytical methodology is proposed to answer the two questions about the molecular and structural features of the acidic xylo-oligosaccharides (XOSs) formed upon the enzymatic hydrolysis of 4-O-methylglucuronoxylan. The shortest acidic XOSs carrying a methylglucuronic acid moiety and the possible distribution of larger products (molecular feature) are instantly found by electrospray ionization mass spectrometry (ESI-MS) in the negative ion mode, which filters the unwanted neutral XOS. The acidic moiety is then unambiguously localized along the xylose backbone (structural feature) by ESI-MSⁿ in the negative ion mode via the selection/activation/dissociation of the product ions formed upon the one-way and stepwise glycosidic bond cleavage at the reducing end. Using the shortest acidic XOS with a known shape generated by glycoside hydrolase family (GH) 10 and GH11 xylanases as a proof of principle, pairs of diagnostic ions are proposed to instantly interpret the MSⁿ fingerprints and localize the acidic moiety along the xylose chain of the activated ion. The original structure of the acidic XOS is then reconstructed by adding as many xylose units at the reducing end as MSⁿ steps. Relying on pairs of ions, the methodology is robust enough to highlight the presence of isomeric products. Mass spectra reported in the present article will be conveniently used as reference data for the forthcoming analysis of acidic XOS generated by new classes of enzymes using this multistage mass spectrometry methodology.

Structures and developmental alterations of N-glycans of zebrafish embryos

Zebrafish is a model organism suitable for studying vertebrate development. We analyzed the N-glycan structures of zebrafish embryos and their alterations during zebrafish embryogenesis to obtain basic data for studying the roles of N-glycosylation. Multiple modes of high-performance liquid chromatography and multistage mass spectrometry were used for structural analysis of N-glycans. The N-glycans from deyolked embryos at 36 hours postfertilization, a mid-pharyngula stage, contained relatively higher amounts of complex- and hybrid-type glycans with LacNAc (Galβ1-4GlcNAc) and/or sialyl LacNAc without additional β1,4-Gal, which are commonly found in mammalian tissues, as well as abundant oligomannose-type glycans. Some of the complex- and hybrid-type glycans possessed various extended LacNAc structures, such as Galβ1-4LacNAc, LacNAc-repeat or unique (+/- dHex)-GalNAcα1-GlcNAcβ1-LacNAc. In contrast, the yolk of the embryo contains predominant oligomannose-type glycans and complex-type glycans with Galβ1-4(Siaα2-3)Galβ1-4(Fucα1-3)GlcNAc antennae. N-Glycan profiles obtained from deyolked embryos at different stages showed stage-dependent variation of complex- and hybrid-type glycans. At gastrula and early segmentation stages, complex- and hybrid-type glycans were minor components, and their antenna structures were mainly sialyl LacdiNAc (Siaα2-6GalNAcβ1-4GlcNAc). From the mid-segmentation to pharyngula stages, those with LacNAc and/or α2,6-sialyl LacNAc antenna structures increased remarkably, and those with α2,3-sialyl LacNAc antenna, core α1,6-Fuc and bisecting GlcNAc modifications increased gradually. These results suggest the presence of mechanisms for regulating the antenna structures of complex/hybrid N-glycan biosynthesis in the phylotypic stage of vertebrate development.

Ion tree-based structure elucidation of acetophenone dimers (AtA) from Acronychia pedunculata and their identification in extracts by liquid chromatography electrospray ionization LTQ-Orbitrap mass spectrometry

Acronychia-type acetophenones (AtA) is a chemical group of compounds of important structural and biological interest, abundant in Acronychia species. However, there are no data available for their characterization using mass spectrometry. In the current work, AtA have been investigated by multistage high resolution mass spectrometry and both electrospray ionization and atmospheric pressure chemical ionization, in positive and negative mode, were utilized for their structure elucidation and identification. The analysis of AtA using a linear ion trap-Orbitrap analyzer enabled the structural determination of key fragment ions and cleavages, which can be used for the structural characterization thereof. A systematic nomenclature based on protonated and deprotonated fragment ions under collision-induced dissociation conditions and decision trees for the structural determination of AtA are proposed. Furthermore, taking advantage of the characteristic fragmentation patterns, a selective Ultra High Performance Liquid Chromatography Electrospray Ionization multistage Mass Spectrometry (UHPLC-ESI(-)-MS(n)) method was developed and successfully applied for the dereplication of known AtA and the identification of potentially new ones in Acronychia extracts. Despite the structure similarity and the presence of isomers, accurate characterization of known and unknown AtA derivatives was possible.

In-chain neutral hydrocarbon loss from crocin apocarotenoid ester glycosides and the crocetin aglycon (Crocus sativus L.) by ESI-MS(n) (n=2, 3)

The stigmas of Crocus sativus L. have been used as spice and colorant agent (i.e. saffron) for more than 4000 years. For an updated structural investigation of the aglycon present in the glycosylated crocetin apocarotenoids (i.e. crocins), seven representative derivatives ranging from one up to five glucosyl-residues with a maximum number of three monosaccharides per glycosylation site (glucose, gentiobiose, gentiotriose and neapolitanose) were isolated and purified by high-performance liquid chromatography. The compounds selected for further mass spectrometric investigation include glucosyl-, bis-glucosyl-, gentiobiosyl-, gentiobiosyl-glucosyl-, bis-gentiobiosyl-, gentiobiosyl-gentiotriosyl- and gentiobiosyl-neapolitanosyl-crocetin. Electrospray ionization in combination with low-energy collision-induced dissociation/tandem mass spectrometry of sodiated crocin precursor ions utilizing either a 3D-ion trap (MS(n) , n = 2, 3) or a QqTOF instrument, with the latter providing accurate mass determination with an accuracy of ±1-3 ppm or better at a resolution of 10,000 (full width at half maximum), was used. Major fragmentation pathways included loss of either one or two carbohydrate substituents leading to the sodiated aglycon without interglycosidic bond cleavage during in MS(2) -experiments. All sodiated precursor ions and major product ions were accompanied by a loss of 92 Da, which was elucidated as C7 H8 -loss from the aglycon by skeletal rearrangement via an eight-membered transition state as previously described for intact C40-carotenoids.