Liquid chromatography mass spectrometry (LCMS)
Red or colorless crystals were thoroughly washed with DDW and dissolved in MeOH. Liquid chromatography mass spectrometry (LC/MS) was performed with the Agilent quadruple LC/MS 6120 series equipped with Reprosil saphir 100, C18, 50 x 2 mm, HPLC column. The eluent solvents were 100% CH3CN. The UV detection was at 254 nm. The column temperature was kept at 50 °C. The flow rate was 0.4 ml/min. The MS fragmentor was tuned on 30 V or 70 V in positive or negative mode.