Identification of Isonitrile‐Containing Natural Products in Complex Biological Matrices Through Ligation with Chlorooximes

Isonitrile-containing natural products have garnered attention for their manifold bioactivities but are difficult to detect and isolate due to the chemical lability of the isonitrile functional group. Here, we used isonitrile-chlorooxime ligation (INC) in a reactivity-based screening (RBS) protocol for the detection and isolation of alkaloid and terpene isonitriles in the cyanobacterium Fischerella ambigua and the marine sponge Axinella sp., respectively. A trifunctional probe bearing a chlorooxime moiety, a UV active aromatic moiety, and a bromine label facilitated the chemoselective reaction with isonitriles, UV-Vis spectroscopic detection, and mass spectrometric analysis. The INC-based RBS allowed for the detection, isolation, and structural elucidation of isonitriles in microgram quantities.