N-Acetyl-L-cysteine (NAC, Spectrum Chemical) was dissolved in milli-Q water, and synthetic honaucin A was solubilized in DMSO. Honaucin A was incubated with NAC in either 2-or 50-fold excess with stirring under argon for 2 h at room temperature (after Wang et al., 2013).22 (link) At the conclusion of the reaction, vial contents were passed over a Bond Elut-C18 SPE column (Agilent) that had been washed with 3 column volumes of methanol and then equilibrated with 3 column volumes of water. The reaction products were subsequently eluted with increasing percentages of methanol. Elutions were dried using rotary evaporation and then reconstituted at a concentration of 1 mg/mL in 50:50 methanol/water. This preparation was analyzed for the presence of the hypothesized addition products via high-resolution MS at the Molecular Mass Spectrometry Facility at the University of California, San Diego. Briefly, reaction products were separated via liquid chromatography using a Phenomenex Kinetex 5 μm EVO C-18 column prior to being introduced to an Agilent 6230 ESI-TOF-MS running in positive mode for high-resolution mass measurement.