An aliquot of 19-epi-DTX2 available from previous work [26 (link)] was dissolved in MeOH (50 µL) in an LC vial insert, formic acid (0.5 µL) was added, and the vial was placed in the sample tray and analysed periodically by LC-MS/MS. A sample of 19-epi-DTX2 in MeOH without acidification was used as a reference standard. Kinetic data were analysed with SigmaPlot 12.5 (Systat, San Jose, CA, USA) by fitting to a 3-parameter exponential decay curve (Figure S5 ).
LC-MS/MS analysis was performed on an Agilent 1260 LC (Palo Alta, CA, USA) coupled to an AB-Sciex (Concord, ON, Canada) 4000 QTRAP MS equipped with a turbospray ionization source. The autosampler temperature was maintained at 10 °C and 2 µL injection volumes were used. A Luna C18(2)HST column (50 × 2 mm, i.d., 2.5 µm; Phenomenex, Torrance, CA, USA) maintained at 20 °C was eluted at 300 µL min−1 with a 7 min linear gradient of 15–100% B, using 5 mM ammonium acetate in H2O (A) and 95% CH3CN (B) at pH 6.8 as the mobile phase. MS detection used selected reaction monitoring with negative polarity electrospray ionization as follows; temperature 500 °C; curtain gas 30 psi; −4.5 kV spray voltage; GS1 40 psi; GS2 60 psi; DP −50 V; and CE values of −65 and −95 eV for the 803.5→255.1 and 803.5→113.1 transitions, respectively, each analysed with a 65 ms dwell time.
LC-MS/MS analysis was performed on an Agilent 1260 LC (Palo Alta, CA, USA) coupled to an AB-Sciex (Concord, ON, Canada) 4000 QTRAP MS equipped with a turbospray ionization source. The autosampler temperature was maintained at 10 °C and 2 µL injection volumes were used. A Luna C18(2)HST column (50 × 2 mm, i.d., 2.5 µm; Phenomenex, Torrance, CA, USA) maintained at 20 °C was eluted at 300 µL min−1 with a 7 min linear gradient of 15–100% B, using 5 mM ammonium acetate in H2O (A) and 95% CH3CN (B) at pH 6.8 as the mobile phase. MS detection used selected reaction monitoring with negative polarity electrospray ionization as follows; temperature 500 °C; curtain gas 30 psi; −4.5 kV spray voltage; GS1 40 psi; GS2 60 psi; DP −50 V; and CE values of −65 and −95 eV for the 803.5→255.1 and 803.5→113.1 transitions, respectively, each analysed with a 65 ms dwell time.