Terpenoids and Bibenzyls from Three Argentine Liverworts

A new rosane diterpenoid, 3α-hydroxy-5,15-rosadien-11-one (3), was isolated, together with a known rosane diterpenoid, 5,15-rosadiene-3,11-dione (4), and an aromadendrane sesquiterpenoid, ent-cyclocolorenone (5), from the Et2O extract of an unidentified Argentine liverwort Anastrophyllum species. Moreover, four known sesquiterpene lactones 6–9 and two known bibenzyls 10, 11 were isolated from the Et2O extracts of Argentine Frullania brasiliensis and Radula voluta, respectively. The structures of compounds 3–11 were determined by the use of NMR techniques.


Introduction
Due to their small morphology, liverworts (Hepaticae) are difficult to classify and identify. However, they are a rich source of terpenoids and aromatic compounds, which can be used to evaluate their chemosystematics [1,2]. In our search for new biologically active substances, we continue to study the chemical constituents of liverworts. Many liverworts are endemic to the southern hemisphere, including Oceania and South America. Recently, we have reported the structures of new sesqui-and diterpenoids from New Zealand liverworts [3]. We also reported the isolation of new sesquiterpenoids 1 and 2 from an unidentified Gackstroemia species from New Zealand [4]. During the course of our investigation of the chemical constituents of three Argentine Jungermanniales species (unidentified Anastrophyllum species, Radula voluta and Frullania brasiliensis), we isolated a new OPEN ACCESS rosane diterpenoid 3 and six previously known compounds: Rosane 4, aromadendrane 5, two eudesmanes 6 and 7, two eremophilanes 8 and 9, and two bibenzyls 10 and 11 ( Figure 1) and characterized their chemical structures. The chemosystematics of these three species from Argentina are discussed.
Fusicoccane and sphenolobane diterpenoids are common chemical components isolated from Anastrophyllum species, e.g., from A. minutum [13], A. aurztum [14] and A. donnianum [15]. These diterpenoids are very characteristic for Anastrophyllum genus belonging to the Jungermanniaceae. However, neither sphenolobane nor fusicoccane were isolated from the present unidentified Anastrophyllum species. Those isolates included naturally rare rosane diterpenoid and aromadendrane sesquiterpenoid. Therefore, the unidentified Anastrophyllum species may be from a chemically different taxon from the other Anastrophyllum species.
Eudesmane and eremophilane sesquiterpene lactones have been isolated from F. brasiliensis (Frullaniaceae) [7] and are considered the most important chemical markers of the Frullaniaceae [1,2,16]. The present F. brasiliensis also contained the same eudesmanolides and eremophilanolides as those reported.
A number of bibenzyls and prenyl bibenzyls were isolated from European, New Zealand, Ecuador and Japanese Radula species (Radulaceae) [1,2,17]. R. voluta also produced bibenzyls 10 and 11, which are ubiquitous components in the Radula species. The Radula including R. voluta is chemically very isolated from the other liverworts examined so far, since the presence of terpenoids is very rare.

Conclusions
A new rosane diterpenoid 3 was isolated from the unidentified Argentine liverwort Anastrophyllum species, together with a known rosane diterpenoid 4 and an aromadendrane sesquiterpenoid 5. The known bibenzyls 10 and 11 and sesquiterpene lactones 6-9 were isolated from Argentine Radula voluta and Frullania brasiliensis.