To demonstrate the utility of RuAAC derivatization in characterizing natural products in crude samples, we prepared a crude ethyl acetate extract from hedgehog mushrooms obtained from a grocery store. We initially thought that these extracts would contain repandiol (C 10 H 10 O 4 ; 10), an unusual di-epoxide internal alkyne natural product with DNA cross-linking activity. We conducted RuAAC by adding 100 mM of azide 2b and 1 mg of catalyst directly to 1 mL of our crude extract. We did not find any evidence for repandiol in our extract: crude extracts showed no evidence of underivatized repandiol, and RuAACderivatized extracts showed no evidence of any predicted repandiol derivatives. However, inspection of the base peak chromatograms of the RuAAC derivatized extracts revealed sev- eral RuAAC-specific, intense peaks. Two of these were for ions with an m/z of 437.1779, differing from the expected mass of a di-triazole derivative of repandiol (m/z of 453.1728) by 15.99 Da, or the mass of one oxygen atom (Figure ).