posted on 2021-05-28, 22:05authored byDong Hao Wang, Hui Gyu Park, Zhen Wang, R. J. Scott Lacombe, Vadim V. Shmanai, Andrei V. Bekish, Karsten Schmidt, Mikhail S. Shchepinov, J. Thomas Brenna
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 PBD-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.