Extraction and Isolation of Bioactive Compound from Warburgia salutaris Bark

The extraction procedure described in Nyaba et al. [16 (link)] was followed. Briefly, the powdered bark of W. salutaris (1 kg) was extracted with dichloromethane (DCM) (1:5 w/v) for three days successively. Whatman (No.1) filter paper was used to filter the crude extract, followed by sample concentration under a reduced pressure (45 °C) to a minimum volume using a Heidolph rotary evaporator (Heidolph Instruments GmbH & CO. KG, Schwabach, Germany). This crude extract was allowed to dry in the fume hood. A portion of the DCM extract was subjected to silica gel column chromatography (60 × 1000 mm; Merck silica gel, 60:0.063–0.200 mm). The eluent system used was hexane: ethyl acetate (8:2), which yielded 35 fractions. The fractions were monitored by Thin Layer Chromatography (silica gel 60 aluminium sheets, F254—Merck, Whitehouse Station, NJ, USA), profiling the fractions into seven combined fractions. The TLC spots were fixed with a solution made of 20% H₂SO₄ in methanol, heated for colour development, and visualized under UV light (254 nm). The fractions were left overnight to until desiccation was achieved. A white powder (NN-01) was obtained from the combined fractions 2–4.