Off-line multidimensional high performance thin-layer chromatography for fractionation of Japanese knotweed rhizome bark extract and isolation of flavan-3-ols, proanthocyanidins and anthraquinones

Abstract

A methodology based on off-line multidimensional thin-layer chromatography was developed for isolation of several secondary metabolites from bark of Japanese knotweed (Fallopia japonica Houtt.) rhizomes. Successive fractionation steps using PLC silica gel and HPTLC silica gel or HPTLC cellulose plates in combination with various developing solvents enabled isolation of (+)-catechin, (-)-epicatechin, (-)-epicatechin gallate, procyanidin B1, procyanidin B2, procyanidin B3, proanthocyanidin B dimer gallate, emodin, emodin-8-O-glucoside and emodin-8-O-malonyl-glucoside. Their identity was confirmed by HPTLC, HPTLC-MSn and for most of them also by 1H NMR and 2D NMR analyses. To the best of our knowledge emodin-8-O-malonyl-glucoside, procyanidins B1 and B2 were for the first time isolated from this plant material. HPTLC and HPTLC-MSn analyses were also performed as support of fractionation/isolation process, leading to first detection of some compounds in bark of Japanese knotweed rhizomes and Japanese knotweed rhizomes in general: procyanidins B1 and B2, methyl derivatives of emodin bianthrone and emodin bianthrone-hexose, resveratrol-malonyl-hexoside and taxifolin derivatives. Characterization of flavan-3-ols and proanthocyanidins was facilitated by post-chromatographic derivatization of the corresponding chromatographic zones with 4-dimethylaminocinnamaldehyde (DMACA) detection reagent.