Pierre Kamnaing

Diarylheptanoids from Myrica arborea

Investigations of the stem and root bark of Myrica arborea (Myricaceae) have yielded two novel diarylheptanoids, myricarborin and 11-O-beta-D-xylopyranosylmyricanol along with the known myricanol and 5-O-beta-D-glucopyranosylmyricanol. The structures of the novel compounds were determined by spectroscopic methods.

An isoflavan-quinone and a flavonol from Millettia laurentii

Abstract A new isoflavan-quinone, 3′,6′-diketo-7-hydroxy-8,2′,4′-trimethoxyisoflavan, named laurentiquinone and a new flavonol, 3,7,4′-trihydroxy-3′,5′-dimethoxyflavone, named laurentinol, have been isolated from the heartwood of Millettia laurentii in addition to two known isoflavones, calycosin and glyricidin. The structures of the new compounds were elucidated from spectral studies. 13 C -NMR spectral data of the known isoflavones are reported here for the first time.

Geranylated flavonoids from Dorstenia poinsettifolia

Abstract Two new geranylated flavonoids, poinsettifolins A and B, were isolated from the extracts of the herb Dorstenia poinsettifolia , and the structures were determined with NMR spectroscopy and mass spectrometry. In addition, the flavone 5,7,4-trihydroxy-8-prenylflavone (licoflavone C), the chalcones 4,2′,4′-trihydroxy-3′-prenylchalcone (isobavachalcone) and isobavachromene, the triterpene butyrospermol, and the carotenoid lutein were isolated.

Diterpenoids from Neoboutonia glabrescens (Euphorbiaceae).

Glabrescin, a daphnane diterpenoid, neoboutonin, a degraded diterpenoid with a novel skeleton, and neoglabrescins A and B, two rhamnofolane derivatives, have been isolated from the stem bark of Neoboutonia glabrescens Prain (Euphorbiaceae), together with the known tigliane derivative, baliospermin, and the known daphnane, montanin. Other constituents include squalene, 3-acetylaleuritolic acid, oleanolic acid and sitosterol, and the phenolic compounds 9-methoxy-1,7-dimethylphenanthrene and 2,3,8-tri-O-methylellagic acid. The structures were assigned on the basis of spectral studies and comparison with published literature data. The structures of neoglabrescins A and B were derived for their acetylated derivatives and, in the case of neoglabrescin A, confirmed by X-ray crystallographic analysis.

Efficient purification of paclitaxel from yews using high-performance displacement chromatography technique.

Paclitaxel was purified using high-performance displacement chromatography (HPDC) technique, but not by the mechanism of HPDC. On small scale, paclitaxel was extracted with methanol from dry needles of Taxus canadensis and was enriched by extracting with chloroform after removing water-soluble hydrophilic components and hexane-soluble hydrophobic components. Then, 93-99% purity of paclitaxel was obtained using the HPDC technique. On large scale, taxanes were enriched by solvent partitioning between acetic acid/MeOH/H(2)O and hexane and extracted with CH(2)Cl(2). Taxanes except paclitaxel were further removed by extracting with methanol-water-trifluoroacetic acid (1.0:98.9:0.1, v/v/v). Applying HPDC technique to water-insoluble substances is problematic as this method requires a highly aqueous solvent system. In order to overcome this incompatibility, a system was set up where paclitaxel, although in low concentration, was extracted by methanol-water-trifluoroacetic acid (10.0:89.9:0.1, v/v/v). Recycling the extracting solvent to ensure minimal volume, the extracted paclitaxel was adsorbed on a C(18) trap column. A C(18) column of 4.6mm internal diameter was then connected to the trap column. The HPDC technique was thus carried out using an isocratic acetonitrile-water-trifluoroacetic acid (30.0:69.9:0.1, v/v/v) mobile phase consisting of a displacer cetylpyridinium trifluoroacetate (3mg/mL). Paclitaxel was co-eluted with the displacer and spontaneously crystallized. The crystal (114mg) showed 99.4% purity and only 10% of paclitaxel in the starting crude extract was lost during the enrichment/purification processes. This large scale purification method was successfully applied to purify paclitaxel from Chinese yew in small scale, suggesting general applicability of the method. This is the first report of purifying a water-insoluble natural product using HPDC technique.

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 C(18) column by using 0.1% trifluoroacetic acid (TFA) or acetic acid/H2O as a carrier and cetylpyridinium trifluoroacetate (or acetate) (1.9mg/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, (1)H NMR and (13)C NMR. This is the first report of one-step HPDC purification of natural and semi-synthetic products from a complex crude extract.