Target-guided isolation of polar antioxidants from Abelmoschus esculentus (L). Moench by high-speed counter-current chromatography method coupled with wavelength switching and extrusion elution mode.

An off-line two-dimensional high-speed counter-current chromatography strategy combined with the wavelength switching technique and extrusion elution mode was successfully developed and applied to the isolation of polar antioxidants from Abelmoschus esculentus (L).Moench. Target-guided by the result of 2,2-diphenyl-1-picrylhydrazyl screening assay, four antioxidants were obtained with purities over 90% through orthogonal high-speed counter-current chromatography separation. UV spectroscopy, mass spectrometry and 1 H NMR spectroscopy were employed to identify their structures, which were assigned as l-tryptophan, quercetin-3-O-sophoroside, 5,7,3',4'-tetrahydroxyflavonol-3-O-[β-d-rhamnopyranosil-(1→2)]-β-d-glucopyranoside, and quercetin-3-O-glucoside. Each monomer exhibited significant antioxidant activity. The results demonstrated that proposed method could be an effective approach to isolate bioactive compounds from complex natural products.