Isolation and identification of phenolic compounds from Gynura divaricata leaves

Abstract

Background: Phenolic constituents were the principle bioactivity compounds exist in Gynura divaricata, little phenolic compounds were reported from the plant previously.

Materials and methods: 60% ethanol extract from the leaves of Gynura divaricata were isolated and purified by column chromatography of Silica gel, ODS and Sephadex LH-20, the structures of the isolated compounds were identified by UV, 1H-NMR, 13C-NMR and MS spectroscopic techniques. Additionally, a high-performance liquid chromatography-diode array detector-electrospray ionization-mass (HPLC-DAD-ESI-MS) analytical method was developed to identify some minor constituents in the n-butanol fraction of the ethanol extract of Gynura divaricata.

Results: Six flavonols and one Dicaffeoylquinic acid were isolated from the leaves of Gynura divaricata, and these compounds were identified as follows: quercetin (1), kaempferol (2), kaempferol-3-O-β-D-glucopyranoside (3), quercetin-3-O-rutinoside (4), kaempferol-3,7-di-O-β-D-glucopyranoside (5), kaempferol-3-O-rutinoside-7-O-β-D-glucopyranoside (6), and 3,5-dicaffeoylquinic acid (7). A total of 13 compounds, including 9 flavonol glycosides and 4 phenolic acids, were tentatively identified by comparing their retention time (RT), UV, and MS spectrum values with those that had been identified and the published data.

Conclusion: This was the first time to use the HPLC-DAD-ESI-MS method to identify the phytochemicals of the genera Gynura. Moreover, compounds (6) and (7) have been isolated for the first time from the genus Gynura.

Keywords: Gynura divaricata DC.; HPLC-DAD-ESI-MS; phenolic constituents.

Figure 1

The procedure of extraction and isolation phenolic compounds from G. divaricata extracts. (a) Silica gel chromatograph eluted with a mixture of chloroform and methanol (from 100:0 to 4:1); (b) Sephadex LH-20 chromatograph eluted with a mixture of chloroform and methanol (1:1); (c) Sephadex LH-20 column eluted with methanol coupled with RP-ODS column gradient eluted with methanol-water (from 40% to 60%, v/v); (d) Sephadex LH-20 column eluted with methanol, (e) RP-ODS column gradient eluted with methanol-water (from 10% to 50%, v/v) coupled with RP-ODS column and isocratic eluted with methanol-water (18%, v/v)

Figure 2

The TIC chromatogram of negative model (a) and HPLC-DAD chromatogram of the n-butanol fraction of G. divaricata extracts (b)

Figure 3

The typical UV spectrum of Kaempferol glucopyranoside derivative (a), Dicaffeoylquinic acid (b), and Quercetin glucopyranoside derivative (c)