2.3. Extraction and isolation
The air-dried roots of D. velutina (5.5 kg) were extracted with CH2Cl2 over a period of 3 days
at room temperature, respectively (2 × 15 L). Removal of the solvent under reduced
pressure provided CH2Cl2 crude extract (75.5 g) that was further separated by column
chromatography over silica gel (Merck Art 7734) and eluted with a gradient of
hexane–EtOAc (100% hexane, 90%, 80%, 70%, 60%, 50% and 40% hexane–EtOAc each
5 L) to give seven fractions (A–G). Fraction A (2.5 g) was purified by a Sephadex LH-20
column (150 g) with 80% CH2Cl2–MeOH (1.5 L) to afford compound 3 (25.5 mg). Fraction B
(1.5 g) was purified by radial chromatography (chromatotron) with 80% hexane–EtOAc
(200 mL) to obtain compound 1 (15.5 mg). Compound 4 (7.8 mg) was obtained from fraction
D (1.1 g) by chromatotron with 80% hexane–EtOAc (200 mL). Fraction F (1.2 g) was also
applied to a Sephadex LH-20 column (150 g) using 80% CH2Cl2–MeOH (2 L) to provide
compound 5 (6.5 mg). Finally, fraction G (1.1 g) was subjected to chromatotron with 80%
hexane–EtOAc (200 mL) to yield compound 2(15.2