Identification and quantification of flavonoids and chromes in Baeckea frutescens by using HPLC coupled with diode-array detection and quadruple time-of-flight mass spectrometry.

This article marks the first report on high-performance liquid chromatography (HPLC) coupled with diode-array detection (DAD) and quadruple time-of-flight mass spectrometry (Q-TOF/MS) for the identification and quantification of main bioactive constituents in Baeckea frutescens. In total, 24 compounds were identified or tentatively characterised based on their retention behaviours, UV profiles and MS fragment information. Furthermore, a validated method with good linearity, sensitivity, precision, stability, repeatability and accuracy was successfully applied for simultaneous determination of five flavonoids and one chromone in different plant parts of B. frutescens collected at different harvest times, and their dynamic contents revealed the appropriate harvest times. The established HPLC-DAD-Q-TOF/MS using multi-bioactive markers was proved to be a validated strategy for the quality evaluation on both raw materials and related products of B. frutescens.

Baeckeins F-I, four novel C-methylated biflavonoids from the roots of Baeckea frutescens and their anti-inflammatory activities.

Baeckea frutescens is an aromatic shrub used in South China as an ornamental and as a spice. Four unusual C-methylated biflavonoids named baeckeins F-I (1-4) were isolated from the roots of B. frutescens. The baeckeins F-I possessed a unique carbon skeleton, a flavonol conjugated with a coumaronochromone molecule via the unusual linkages of C-2-C-8 and C-3-O-C-7. Their structures were elucidated by analysis of the 1D ((1)H/(13)C) and 2D NMR (HSQC/HMBC/NOESY) and HR-ESI-MS spectroscopic data, and the absolute stereochemistry for chiral carbons of C-2 and C-3 was established by CD spectrometry combined with quantum chemical calculations. Baeckeins F-I (1-4) were also evaluated for their anti-inflammatory activities by detecting the NO production of LPS-induced RAW264.7 murine macrophage cell line; baeckein I (4) with the ß-d-glucose unit and configuration of (2R,3R) exhibited the highest NO inhibitory activity (IC50=15.2 µM), which was similar to that of the positive control indomethacin.

Baeckein E, a new bioactive C-methylated biflavonoid from the roots of Baeckea frutescens.

A phytochemical study of Baeckea frutescens afforded a new biflavonoid named as baeckein E (1), along with four known C-methylated flavonols, baeckeins A (2) and B (3), 6-methylquercetin (6) and 6-methylquercetin-4'-O-ß-D-glucopyranoside (7), and two known biflavonoids baeckeins C (4) and D (5). The structure of compound 1 was elucidated on the basis of spectroscopic analysis, including HR-ESI-MS, 1D and 2D NMR spectra, and the absolute configurations of C-2 and C-3 for compound 1 were assigned by circular dichroism spectrometry combined with quantum chemical calculations. The antioxidant and cytoprotective activities of compounds 1-7 were also investigated.