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 andalgae, including the brown algaUndaria pinnatifida, also known aswakame. The systematic recognition of As-PL has been hamperedby the lack of standard and of qualitative methods to establish thecarbon-carbon double bond positions of unsaturated fatty acylchains. Here, the epoxidation reaction of fatty acyl substituents ofAs-PL was carried out with high selectivity bymeta-chloroperox-ybenzoic acid and the C-C double bond localization wasestablished by collision-induced dissociation of epoxidized speciesas deprotonated molecules, [epoM-H]-. Reversed-phase liquidchromatography (RPLC) separation and a sequential triple-stageMS (i.e., MS3) analysis of unsaturated and epoxidized As-PL werevery helpful to characterize the carbon-carbon double bond locations of bothsn-1 andsn-2 fatty acyl chains, starting from adiagnostic product ion pair with 16.0 Da mass difference. These results indicate that intact As-PL can be annotated in terms of fattyacyl chain composition and in terms of their C-C double bond position(s). Interestingly, hexadecenoic (16:1 Delta 9) and octadecenoic(18:1 Delta 9) along with octadecadienoic (18:2 Delta 9,12) and octadecatrienoic (18:3 Delta 9,12,15) were found to be the most abundantunsaturated fatty acyl chains of As-PL in the brown alga wakame, thus confirming it as a good source of essential fatty acids with abalanced omega 6/omega 3 ratio. Although the toxicity of As-including metabolites of algal As-PL is still a matter of debate and needs to bestudied in more detail, the described approach can be exploited to assess if As-PL could contribute to the supply of essential fattyacids related to the use of algae as nutritious food