The position of carbon-carbon double bond(s) in fatty acid lipid molecules crucially affect their structure, reactivity, biological function, and nutritional value.  The accurate identification of double bond(s) position within lipid molecules has been investigated using a variety of specialized mass spectrometric techniques, but many limitations remain, particularly for rare and unusual lipids, and there is a great potential for approaches that involve a derivatization step prior to detection and analysis. Our work has focused on developing a simple, rapid, and reliable technique based on  a cross metathesis approach for derivatizing double bond(s) in unsaturated lipids. We utilize a highly reactive allyl sulfone group conjugated to a hydrazinylpyridine-derived triazaborolopyridinium fluorescent probe (HPY-dye) that undergoes efficient cross metathesis with unsaturated lipid substrates, generating unique signature fluorescent fragments that are analyzed on HPLC/MS. The unsaturated fatty acid components yield corresponding labeled “HPY-head groups” and aliphatic “HPY-tails” as products suitable for optical chromatographic detection due to their strong absorption of UV light, and accurate mass analysis due to their characteristic boron isotopic pattern. Double bonds in long chain mono-unsaturated fatty acids are readily and unambiguously identified. Convenient identification of omega-3, omega-6 or omega-9 fatty acids was possible with this approach analyzing the aliphatic products from labeling at the terminal double bond position. This methodology was successfully applied to the omega fatty acid composition characterization of a series of triacylglycerol mixtures. Secondary metathesis processes can occur with polyunsaturated fatty acids, and we characterized the product distribution and computationally evaluated the energy profiles for competing ring closing metathesis pathways with linoleic and linolenic fatty acids.<br/>

Cross metathesis labeling with fluorescent probes for the identification and quantitation of unsaturated lipids

ACS Fall 2020 Virtual Meeting

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