Separation of 25R/S-ergostane triterpenoids in the medicinal mushroom Antrodia camphorata using analytical supercritical-fluid chromatography

Ergostanes are major bioactive constituents of the medicinal mushroom Antrodia camphorata. These tetracyclic triterpenoids usually occur as 25R/S epimeric pairs, which renders their chromatographic separation difficult. In this study, we used analytical supercritical-fluid chromatography (SFC) to separate seven pairs of 25R/S-ergostanes from A. camphorata. The (R)- and (S)-forms for each of the seven pairs could be well resolved (Rs > 1.3) on a Chiralcel OJ-H column (4.6 × 250 mm, 5 μm, chiral), eluted by 10% MeOH in CO2 at 2 mL/min with a back pressure of 120 bar and a column temperature of 40 °C. Particularly, this chiral-SFC method could rapidly and efficiently separate low-polarity epimers like antcin A and antcin B, which were very difficult for RP-HPLC. A 3-min preparative-scale method was established to purify (25S)- and (25R)-antcin A for the first time. However, OJ-H column suffered from peak overlapping of different pairs of ergostanes. We found that Princeton 2-ethylpyridine column (2-EP, 4.6 × 250 mm, 3 μm, achiral) could effectively separate different pairs, although the resolutions for 25-R/S forms of each epimeric pair were not as good as OJ-H column. Meanwhile, all the (25S)-forms showed stronger retentions than the corresponding (25R)-epimers on the 2-EP column. These results demonstrated different selectivity of chiral- and achiral-SFC in separating 25R/S-ergostane epimers. Aside from high separation efficiency, SFC also showed advantage over HPLC in short analysis time and low consumption of organic solvents. Finally, both OJ-H and 2-EP columns were used on analytical SFC to separate 25R/S-ergostanes in an extract of A. camphorata.