Oleoside type secoiridoids from the flowers of Syringa dilatata and their potential as anti-inflammatory agents

Syringa plants, which have good fragrance and beautiful appearance, are cultivated worldwide. Also, this plants have been reported to contain various secondary metabolites such as iridoids, lignans, and phenylethanoids. In particular, yringa plants contain a large amount of iridoids that have pharmacological activities. Due to the effectuation of the Nagoya Protocol, securing of biological resources has become very important. For this reason we have been interested in S. dilatata, only a Korea native species of its genus. No study has been reported for components and activities of S. dilatata flower. Therefore, the present study focused on the isolation and identification of active compounds from this plant, as well as examination of the anti-inflammatory effect of the isolated compounds.

Dried flowers of S. dilatata were extracted with aqueous MeOH, and the concentrated extract was partitioned into EtOAc, n-BuOH, and H₂O fractions. Repeated SiO₂, ODS, and Sephadex LH-20 column chromatographies on n-BuOH fraction, led to isolation of eight new iridoids (6-13) and nine known ones (1-5, 14-17). From the results of spectroscopic data the chemical structures were identified without ambiuity. All compounds were isolated for the first time from S. dilatata flowers in this study.

Some compounds showed significantly NO inhibition in LPS-stimulated RAW 264.7 macrophages. In addition, quantitative analysis of iridoids in the S. dilatata flowers was conducted through HPLC experiments. These results supported that the iridoids isolated from the S. dilatata flowers and its extract are potential as anti-inflammatory agents.

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