A novel off-line multi-dimensional high-speed countercurrent chromatography strategy for preparative separation of bioactive neolignan isomers from Piper betle. L.

Separation and purification of naturally occurring isomers from herbs are still challenging. High-speed counter-current chromatography (HSCCC) has been applied to isolate natural products. In this study, an off-line multi-dimensional high-speed counter-current chromatography (multi-D HSCCC) strategy was developed utilizing the in situ concentration technique with online storage recycling elution to rapidly separate bioactive isomeric neolignans from chloroform-partitioned samples of the plant Piper betle L. In the procedure, the crude sample (105 mg) was implemented using the online storage recycling technique in a two-phase solvent system composed of petroleum ether-ethyl acetate-methanol-water (7: 5: 12: 3), which first simply afforded a neolignane kadsurenone (1, 5.3 mg) and its epimer (-)-denudatin B (2, 6.4 mg). Then, the remains fr a was subjected to the second-dimensional HSCCC elution using the in situ concentration technique with online storage recycling technique in another solvent system of petroleum ether-ethyl acetate-methanol-water (5: 5: 11, 15). As a result, kadsurenin I (3, 0.6 mg) and its regioisomer pibeneolignan C (4, 5.0 mg), together with the fractional remaining fr b and fr c, were obtained. Thirdly, the fr c was reloaded to allow the HSCCC for recycling elution with the former solvent system employing the in situ concentration strategy and yielded a pair of epimers, (7R,8S,1'S)-1'-allyl-5-methoxy-8-methyl-7-piperonyl-7,8,3,6-tetrahydro-2-oxobenzofuran (5, 10.2 mg), and 3-epi-(-)-burchullin (6, 2.6 mg). Finally, the three pairs of less amount and the structurally similar isomers 1-6 were isolated from the crude fraction of P. betle with a high HPLC purity of over 95.0 % for compound 2, 4-6 and 92.5 % for compound 1, 91.0 % for 3, while the purity of 1 and 3 in 1H NMR were 89.9 % and 91.1 %, respectively. The whole isolation process was quick and efficient. Compounds 1, 2, 4 and 5 showed significantly synergistic activities combining several antibiotics against five drug-resistant Staphylococcus aureus with FICIs from 0.156 to 0.375. This novel off-line multi-dimensional HSCCC strategy could be broadened to application for the rapid separation of complex natural products.