Enrichment method fishes unknown metabolites out of complex mixtures

Unlike proteins, biological small molecules aren’t made via a template-driven process. Thus, identifying the full complement of an organism’s metabolites can be difficult. Joshua A. Baccile of the University of Tennessee, Knoxville, Frank C. Schroeder of Cornell University, and coworkers have developed an enrichment method to make it easier to identify previously unknown metabolites (J. Am. Chem. Soc. 2020, DOI: 10.1021/jacs.0c06877). In their method, which they call deep interrogation of metabolism by enrichment, or DIMEN, they pull metabolites from a targeted pathway out of a sample using click chemistry. The method depends on an alkyne-modified small-molecule building block and a solid support modified with an azido-valerate linker. Any metabolic products of the alkyne-modified small molecule are extracted from a sample by reaction with the azide solid support and subsequently cleaved for mass spectrometric analysis. The solid support is designed so that enrichment physically separates metabolites of interest from the complex metabolic background and installs a reporter ion for the analysis. The researchers focused on ascarosides, a class of signaling molecules produced by Caenorhabditis elegans. By feeding the worms an alkyne-modified ascaroside building block (shown), the researchers were able to identify hundreds of previously unknown metabolites made with it. The approach appears to be broadly applicable as long as small molecules of interest can be modified with alkynes without impeding enzymatic processing.