Fatty acid neutral losses observed in tandem mass spectrometry with collision‐induced dissociation allows regiochemical assignment of sulfoquinovosyl‐diacylglycerols

Abstract

A full characterization of sulfoquinovosyldiacylglycerols (SQDGs) in the lipid extract of spinach leaves has been achieved using liquid chromatography/electrospray ionization-linear quadrupole ion trap mass spectrometry (MS). Low-energy collision-induced dissociation tandem MS (MS/MS) of the deprotonated species [M - H](-) was exploited for a detailed study of sulfolipid fragmentation. Losses of neutral fatty acids from the acyl side chains (i.e. [M - H - RCOOH](-)) were found to prevail over ketene losses ([M - H - R'CHCO](-)) or carboxylates of long-chain fatty acids ([RCOO](-)), as expected for gas-phase acidity of SQDG ions. A new concerted mechanism for RCOOH elimination, based on a charge-remote fragmentation, is proposed. The preferential loss of a fatty acids molecule from the sn-1 position (i.e. [M - H - R(1)COOH](-)) of the glycerol backbone, most likely due to kinetic control of the gas-phase fragmentation process, was exploited for the regiochemical assignment of the investigated sulfolipids. As a result, 24 SQDGs were detected and identified in the lipid extract of spinach leaves, their number and variety being unprecedented in the field of plant sulfolipids. Moreover, the prevailing presence of a palmitic acyl chain (16:0) on the glycerol sn-2 position of spinach SQDGs suggests a prokaryotic or chloroplastic path as the main route for their biosynthesis.

Antiviral Sulfoquinovosyldiacylglycerols (SQDGs) from the Brazilian Brown Seaweed Sargassum vulgare

“…The structure was confirmed comparing our data to the fragmentation pathway already described by Zianni and coworkers [25] for a similar SQDG isolated in a lipid extract from spinach leaves.…”

Unambiguous regiochemical assignment of sulfoquinovosyl mono‐ and diacylglycerols in parsley and spinach leaves by liquid chromatography/electrospray ionization sequential mass spectrometry assisted by regioselective enzymatic hydrolysis

“…In the Plantae kingdom two species have been largely studied in terms of their sulfolipid content: Arabidopsis thaliana (widely used as a model organism in plant biology) and Spinacia oleracea . It is known that spinach leaves contain the largest amount of SQDG, followed by parsley ( Petroselinum crispum ); for this reason, both these plants were chosen as a target for the present investigation.…”

“…Mass spectrometry (MS) has played a key role in the identification of SQDG in recent years and several different approaches have been proposed, including matrix‐assisted laser desorption/ionization with quadrupole ion‐trap low‐energy collision‐induced dissociation and time‐of‐flight MS (MALDI‐QIT‐TOF‐CID‐MS n ), fast atom bombardment (FAB)‐CID‐MS/MS, electrospray ionization (ESI)‐triple quadrupole CID‐MS/MS, ESI‐linear ion trap CID‐MS/MS, and ESI‐Orbitrap MS . MS‐based regiochemical assignment is particularly challenging in the case of sulfolipids because (i) the collision energy value during CID‐MS/MS investigation can significantly affect fragmentation pathways and (ii) no commercial standards with known regiochemistry are available.…”

Natural Products from Microalgae with Potential against Alzheimer’s Disease: Sulfolipids Are Potent Glutaminyl Cyclase Inhibitors

“…Sulfoquinovosyldiacylglyceride (1,2-di- O -acyl-3- O -(6′-deoxy-6′-sulfo- d -glycolpyranosyl)-sn-glycerols) are esterified with two fatty acids. In their mass spectra the neutral losses of the respective fatty acids (palmitic acid, linoleic acid or linolenic acid) with the formation of the characteristic fragment C 6 H 9 O 7 S at m/z 225 may be found [29,30,31,32]. The natural SQDGs have an α-anomeric glycoside conformation [33].…”

“…Taking this into account [34], possibly the higher peak intensity of fragment ion [b] at m/z 537.2 in comparison to fragment ion [a] suggests the position of the palmitic acid to be at the sn-2-postion. Based on this and other references the positions postulated in the literature are assumed also here [29,35,36,37]. Thus for compound 1 at sn-1-position linolenic acid (C18:3) and at sn-2-position palmitic acid (C16:0), for compound 2 at sn-1-position linoleic acid (C18:2) and at sn-2-position palmitic acid (C16:0) and for compound 3 at sn-1-position and sn-2-position palmitic acid (C16:0) are proposed.…”