Isolation and characterization of new phenanthrenes from Juncus inflexus and their chemotaxonomic significance

According to the literature data, the most commonly occurring secondary metabolites of the Juncaceae family are phenanthrenes, flavonoids, terpenoids, phenolic acids, sterols and coumarins. Admittedly, phenanthrenes are the major bioactive components of these species. Previously, the cytotoxic, antimicrobial, antiviral and anti-inflammatory activities of phenanthrenes were reported. Our previous phytochemical studies revealed the presence of two new 9,10-dihydrophenanthrenes along with 7 known phenanthrenes in Juncus inflexus. In continuation of our studies on this species, in the present paper we report on the isolation and identification of new phenanthrenes from this plant. The root parts of the plant were extracted with methanol. After evaporation, the extract was subjected to solvent-solvent partitioning with n-hexane, CH₂Cl₂ and ethyl acetate. The combined n-hexane and CH₂Cl₂ fractions was chromatographed by a combination of different methods, including CC, VLC, preparative TLC and Sephadex LH-20 gel filtration. The structure elucidation was carried out by extensive spectroscopic analysis, using one- and two-dimensional NMR spectroscopy and HRMS experiments. Absolute configurations of the compounds were also determined by CD measurements.

The results allowed the identification of one new 9,10-dihydrophenanthrene, and one new dimeric phenanthrene. These compounds were substituted with methyl, hydroxyl, methoxy and vinyl groups. Most of the phenanthrenes isolated previously from Juncus species are vinyl derivatives, so these compounds could serve as chemotaxonomic markers for the genus. Interestingly, the position of vinyl group in phenanthrenes isolated previously from this genus is C-5, while in case of our compounds the vinyl groups are connected at positions C-6, C-7 or C-8, too.

Acknowledgement: This work was supported by the Hungarian Scientific Research Fund (OTKA K109846) and a János Bolyai Research Scholarship of the Hungarian Academy of Sciences.

Keywords: phenanthrene, dimeric phenanthrene, Juncaceae, Juncus inflexus.