Alkynes, especially from plants and fungi, are components of most human diets. Some of these unusual specialized metabolites have demonstrated bioactivities, in humans or in their native host. These molecules are often lipid-derived, but the precise pathways by which alkynes are biosynthesized by our food or broken down in our bodies are mostly unknown. Many natural alkynes ionize poorly, are not particularly thermally stable, and are difficult to reliably disambiguate from isomeric dienes, especially in complex samples. Thus, a central challenge in tracking the metabolic origins and fates of dietary alkynes is the lack of a sensitive and specific means for their analysis. Here, we present an LC-MS derivatization method for naturally occurring internal alkynes that is based on ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC). We show that RuAAC, adapted from the synthetic chemistry literature, can be applied to complex samples at analytical scales, in a variety of solvents, without requirement for rigorous anoxia or dryness. It generates 1,4,5-trisubstituted triazoles from internal alkynes, and that it can be used to confirm the identity of putative alkynes in complex samples. Furthermore, the triazole derivatives ionize up to 32,000-fold more efficiently than the parent compounds, meaning that our RuAAC derivatization can improve sensitivity for LC-MS analysis. We demonstrate the utility of the method by applying it to the elucidation of the biosynthetic pathway of a tomato- and carrot-derived alkyne, falcarindiol, and to the isolation of a new dietary alkyne identified in hedgehog mushroom.

The alkynes we eat: Where do they come from and how do we identify them?

2019 Fall National Meeting

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