A novel Aryldihydronaphthalene Lignan from Linum perenne L

In the course of our study on the chemical diversity of lignans in the genus Linum, we investigated the aerial parts of L. perenne L. By HPLC-MS, the cytotoxic, antiviral and anti-inflammatory arylnaphthalene lignan justicidin B, previously reported by us as a constituent of L. austriacum [1] was identified. Further peaks corresponded to lignans hitherto unreported for Linum species. Compound 1 was found to be an aryldihydronaphthalene lignan with a hitherto unreported additional oxepine ring connecting the two aromatic moieties. Its structure was unambiguously proven by heteronuclear 2D-NMR (HSQC, HMBC). Compound 2 was previously obtained synthetically [2] but not reported as a natural product up to present. The structure of 3 has not been reported before, to the best of our knowledge. Compound 4 has previously been found as a natural product in Cleistanthus collinus (Euphorbiaceae) [3].

It is noteworthy that such presumable biogenetic intermediates between aryltetralin-type lignans (e.g. podophyllotoxin) and arylnaphthalenes (e.g. justicidin B), found in other members of the genus, were now found in a Linum species together with an arylnaphthalene for the first time. Compound 1, moreover, deserves special mentioning since its novel ring system including a dibenzo[b,e]oxepine structure has not been reported as part of a lignan or natural product so far, to the best of our knowledge. Isolation of further lignans from L. perenne and establishment of the absolute stereochemistry of 1-4, as well as evaluation of their biological activity, is in progress.

Acknowledgements: TJS acknowledges DFG grant Schm 1166/2–2. We thank Dr. H. Luftmann, Organic Chemistry, Münster, for HR MS spectra.

References: 1. Mohagheghzadeh, A. et al. (2002), J. Nat. Prod. 65: 69–71. 2. Stevenson, R. et al. (1971), J. Org. Chem. 36: 3453–5. 3. Ajaneyulu, A. S. R. et al. (1981), Tetrahedron 37: 3641–52.