Toward Quantitative Sequencing of Deuteration of Unsaturated Hydrocarbon Chains in Fatty Acids

This is the authors' abstract. We don't add key points for this paper.

No general method currently is available for the quantitative determination of deuterium (D) at C positions along a hydrocarbon chain. Bis -allylic deuterated highly unsaturated fatty acids (D-HUFA) are a novel class of drugs stabilized against H-abstraction-mediated oxidation by deuteration at the most labile positions. Ru-based catalytic deuteration overcomes the limited scale of bis -allylic D-HUFA production by total organic synthesis; however, it produces a complex mixture of bis -allylic D isotopologues and isotopomers, requiring detailed sequencing for characterization. We report here adaptation and application of the Paternó–Büchi (PB) reaction of 2-acetylpyridine to a series of D-HUFA with analysis by shotgun lipidomics to determine position-specific quantitative D abundances. Sodiated PB D-HUFA result in diagnostic ions of high abundance upon collision-induced dissociation (CID) activation, enabling sensitive differentiation and quantification of D fraction at each bis - and mono -allylic position for each isotopologue. Catalytically deuterated isotopologues D5-7 linolenic acid (D5-7 LnA), D6-8 arachidonic acid (D6-8 ARA), D7-9 eicosapentaenoic acid (D7-9 EPA), and D9-11 docosahexaenoic acid (D9-11 DHA) incorporate 80–98, 95–100, 81–100, and 83–100% D at their bis -allylic positions, respectively. D-HUFA isotopologues having D number greater than or equal to bis -allylic sites (e.g., D10–DHA or D11–DHA) deuterated >95% at bis -allylic positions, except for D-LnA. The mono- allylic position near the methyl end deuterates to a much greater extent than the mono- allylic position near the carboxyl end, and both positions deuterate only when bis -allylic D is near-saturated. This method enables rapid, accurate characterization of position and isotopomer-specific D composition and enables sequencing along the chain.