Employing Sterculic Acid–a naturally occurring 1, 2-cyclopropene fatty acid–for live-cell imaging of lipids by inverse electron-demand Diels-Alder reaction

To allow the study of unsaturated free fatty acids in live cells, we here report the use of sterculic acid, a 1,2-cyclopropene containing oleic acid analogue, as a bioorthogonal probe. We here show that this lipid can be readily taken up by dendritic cells without toxic side-effects, and that it can subsequently be visualised in live cells using an inverse electron-demand Diels-Alder (IEDDA) reaction with quenched tetrazine fluorophores. Furthermore, this reaction can be integrated into a multiplexed bioorthogonal reaction workflow by combining it with two sequential copper-catalysed Huisgen ligation reactions. This allows for the study of multiple biomolecules in the cell simultaneously by multimodal confocal imaging. Aside from lipid imaging, the uptake and protein modification of sterculic acid can be studied in live cells via chemical proteomics.