Gas phase reactivity of isomeric arylglycosides towards amines. A chemical ionization mass spectrometry and tandem mass spectrometry study

Abstract

Chemical ionization mass spectrometry (MS) and tandem mass spectrometry (MS/MS) experiments have been performed for the structural characterization and isomeric differentiation of two series of C-and O-linked arylglycosides with potential antioxidant activity. Different amines have been used for producing gas phase chemical ionization. Depending on their proton affinity and steric hindrance, adduct ions with different stability are formed. The most stable adducts are produced by ethylamine and they have been extensively structurally characterized by experimental and theoretical approaches. Energy resolved chemical ionization tandem mass spectrometric experiments have allowed unambiguous characterization and differentiation of both the anomers differing at the configuration of the glycosidic C(1) atom, and regio-and structural isomers at extremely low concentrations, typical of mass spectrometry. This study has shown that amine chemical ionization mass spectrometry and MS/MS are powerful and versatile tools for the structural characterization of arylglycosides. A growing interest in the discovery, characterization, and isomeric differentiation of new glycosides having enhanced, selective, and distinctive properties has been developed in the last decade. Owing to their complexity, the set-up of methods characterized by high selectivity, specificity, and sensitivity has a crucial role. Most of these are based on mass spectrometry (MS) and MS/MS approaches [4 -9]. Gas-phase stable complexes obtained by chemical ionization (CI) [10] with different reagents have been used for the structural characterization and differentiation of oligosaccharides and glycosides [11][12][13][14][15][16][17][18][19].The linkage between a sugar and a substituted phenol produces arylglycosides that can show different antioxidant properties and can be used as protective agents against oxidative stress processes in vivo [20]. Chemical modifications of their skeleton allow enhancement and modulation of their properties and antioxidant activities.We recently synthesized C-and O-glycopyranosyl arenes (1-3, Scheme 1) as potential antioxidant agents [21]. They are analogous to 2(3)-tert-butyl-4-hydroxyanisole with increased water solubility due to the presence of the sugar moiety. These compounds show different types of isomerism. Inside each series, the compounds are positional isomers, differing in the position of the tert-butyl group; members of Series 1 and 3, and Compound 2 are structural isomers. Generally they are ␣-anomers, while for some of them, i.e., 2 and 3b, both the ␣ and ␤ anomers are available. All the compounds have the same molecular weight of 362 u.The study of these compounds in the gas phase is particularly difficult and complex. Under electron ionization only fragment ions are detected and no information on the whole molecule can be obtained. Recently, we have been able to differentiate these compounds by using the self-ionization technique occurring in an ion trap mass spectrometer [22]. On the other hand, this technique ...

The power of energy‐resolved tandem mass spectrometry experiments for resolution of isomers: the case of drug plasma stability investigation of multidrug resistance inhibitors

“…The product ion scan analyses were acquired in the range from m/z 50 to 650, scan time 600 ms, argon was used as collisional gas and the collision energy was increased stepwise in the range 5 to 50 V. A series of energy-resolved tandem mass spectrometry (ERMS) experiments were performed to study the fragmentation of each analyte and construct their breakdown curves. [14,15] The breakdown curves data were obtained by introducing working solution 1 of each analyte, via syringe pump at 10 μL min À1 ; the protonated molecule was isolated and the abundances of product ions were monitored. In order to establish the optimal conditions of the collision-induced dissociation (CID) process, the breakdown curve of GDE6 was repeated at different partial pressures of argon (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mTorr as read by the instrument control).…”

Evaluation of the α‐phenylvinyl cation as a chemical ionization reagent for the differentiation of isomeric substituted phenols in an ITMS

“…The CI-CID spectrum of the adduct ion at m/z 225 from the 2,6-dimethyl isomer (7) shows a characteristic loss of a methyl radical generating ions at m/z 210. The 2,4-dimethyl isomer (8) shows a unique ion at m/z 123, whereas the 3,5-dimethyl isomer (9) displays both this ions with a very low intensity. 2,6-Dimethyl isomer can be further distinguished from the other two on the basis of the low intensity of the ion at m/z 197, attributed to the loss of 28 Da.…”

Structural characterization and regiochemical differentiation of α-cyanoethylindole isomers in the gas phase

“…As the gas phase reactions occurring inside a mass spectrometer are strictly related to the structure of a compound, mass spectrometry (MS) and tandem mass spectrometry (MS/MS) are very powerful tools for isomeric characterization and differentiation. Their application in the field of heterocycles, and in particular in the characterization of the indole skeleton, has been successful [4 -12].In the frame of a research aimed at studying the gas phase ion chemistry of heterocycles [13][14][15][16], we wish to report here on a study devoted to the characterization and differentiation of a series of ␣-cyanoethyl-3-methylindoles 1-4 and a 3H-indole derivative 5 (Scheme 1) obtained by photochemical reactions [17].All these compounds have the same formula and molecular weight equal to 184 u. Compounds 1-4 are regio isomers, differing in the position of the ␣-cyanoethyl substituent on the heterocyclic system.…”

“…In the frame of a research aimed at studying the gas phase ion chemistry of heterocycles [13][14][15][16], we wish to report here on a study devoted to the characterization and differentiation of a series of ␣-cyanoethyl-3-methylindoles 1-4 and a 3H-indole derivative 5 (Scheme 1) obtained by photochemical reactions [17].…”