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

• Published in: Journal of the American Society for Mass Spectrometry Vol. 33; no. 5; pp. 823 - 831
• Main Authors: Coniglio, Davide, Ventura, Giovanni, Calvano, Cosima D, Losito, Ilario, Cataldi, Tommaso R. I
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 04-05-2022
• Subjects: Animals; Arsenates; Carbon; Monosaccharides; Phospholipids - analysis; Plant Extracts; Seaweed; Undaria - chemistry; double bonds; seaweeds; reversed phase liquid chromatography; unsaturated fatty acids; arsenosugar phospholipids; multistage mass spectrometry
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1021/jasms.2c00006

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.