Identification of lignans and quality assessment in Dendrobium officinale under different cultivation modes

Lignans have attracted much attention from researchers because of their wide distribution and industrial applications in plants, as well as the remarkable diversity of their biological activities. As the literature has mainly focused on the extraction and identification of monomeric compounds of lignans, most lignans in Dendrobium officinale, a traditional Chinese medicine with a long cultivation history and rich sources, have not been detected using quality control methods. The aim of this study was to identify the lignans in Dactilon officinale.

High-performance liquid chromatography (HPLC) coupled with diode array detection and HPLC multiple-stage tandem mass spectrometry was used to identify the chemical constituents of D. officinale. Simultaneously, the characteristic chromatograms of D. officinale were established. Additionally, a method was established to determine the content of syringaresinol-4,4'-di-O-β-D-glucoside, syringaresinol-4-O-β-D-glucoside and syringaresinol.

Thirty-three lignans, including 17 tetrahydrofuran lignans, two dibenzylbutane lignans, three aryl tetrahydronaphthalene lignans and 11 8-O-4'-neolignans, were tentatively identified from the methanol extract of the stems of D. officinale. This is the first report of 8-O-4'-neolignans from D. officinale. In addition, a total of eight characteristic peaks were marked in characteristic chromatograms, which were identified as lyoniresinol-9'-O-β-D-glucoside, syringaresinol-4,4'-di-O-β-D-glucoside, 8-hydroxy-syringaresinol-4-O-β-D-glucoside, 5,5'-dimethoxy-lariciresinol-4-O-β-D-glucoside, syringaresinol-4-O-β-D-glucoside, 4-hydroxy-3,3',5,5'-tetramethoxy-8,4'-oxyneoligna-7'-ene-9,9'-diol-9-O-β-D-glucoside, 4-hydroxy-3,3',5,5'-tetramethoxy-8,4'-oxyneoligna-7'-ene-9,9'-diol-4-O-β-D-glucoside and syringaresinol. Our results showed that no significant difference occurred in lignan composition among the 99 batches of D. officinale from different sources. However, the peak areas of the lignans of D. officinale planted under simulated wild culture were generally higher than those in greenhouses, and showed an upward trend with the increase in growth years. The average contents of syringaresinol-4,4'-di-O-β-D-glucoside, syringaresinol-4-O-β-D-glucoside and syringaresinol were 10.112-179.873, 51.227-222.294 and 6.368-120.341 μg/g, respectively.

This study provided a basis for improving the quality control of D. officinale and could provide references for the identification of lignans in other Dendrobium species.