One-step purification of palmatine and its derivative dl-tetrahydropalmatine from Enantia chlorantha using high-performance displacement chromatography

Palmatine and its reduced form, dl-tetrahydropalmatine are a group of isoquinoline alkaloids that have been reported to display a variety of biological and pharmacological activities. Both drugs are hydrophilic and are difficult to be purified by conventional purification methods of natural products. A high-performance displacement chromatography (HPDC) method successfully purified palmatine and its semi-synthetic derivative dl-tetrahydropalmatine from crude extract of the African medicinal plant Enantia chlorantha. The crude extract from the root bark of E. chlorantha was fractionated on an analytical reversed-phase C18 column by using 0.1% trifluoroacetic acid (TFA) or acetic acid/H2O as a carrier and cetylpyridinium trifluoroacetate (or acetate) (1.9 mg/mL) in 0.1% TFA (or acetic acid)/H2O as a displacer. Palmatine was quantitatively purified at >98% purity in the fully developed displacement mode. dl-Tetrahydropalmatine was semi-synthesized by NaBH4 reduction from crude palmatine and directly purified by HPDC. Both palmatine and dl-tetrahydropalmatine were identified by high-resolution electrospray tandem mass spectrometry, 1H NMR and 13C NMR. This is the first report of one-step HPDC purification of natural and semi-synthetic products from a complex crude extract.