Abietane and nor-abitane diterpenoids from the roots of Salvia rhytidea

Background The genus Salvia is a rich source of structurally diverse terpenoids. Different species of the Salvia have been used in folk medicine of Iran and therefore attracted the attention of researchers for exploring their chemical constituents. In a project directed at structurally interesting bioactive metabolites from Iranian Lamiaceae, we studied Salvia rhytidea. Results Fractionation of the petroleum ether extract of the root of S. rhytidea led to the isolation of a new 20-nor-abietane diterpenoid (1), together with seven known compounds, comprising five abietane diterpenoids (2–6), and two rearranged abietanes (7, 8). Their structures were established by a combination of 1D and 2D NMR. Conclusions Our results showed that the root of S. rhytidea could be considered as a new and rich source of different types of abietane and rearranged abietane diterpenoids.

Taxodione (3) is a diterpenoid with quinone methide skeleton which was reported from different genus like Taxudium, Clerodendrum, and Salvia (Machumi et al. 2010;Kolak et al. 2009;Kusumoto et al. 2009). Different biological properties have been reported for this compound, including antibacterial (Yang et al. 2001 (Topçu and Gören 2007), and anticholinesterase activities (Topcu et al. 2013). Moreover, cytotoxic and tumor inhibitory properties of taxodione have been investigated in in situ and in vivo experiments (Kupchan et al. 1969;Ulubelen et al. 1999;Abou Dahab et al. 2007). The mechanism of action of taxodione for its cytotoxic properties was investigated in several articles with focus on its DNA binding and DNA damaging character (Zaghloul et al. 2008), and its enzyme inhibitory action (Hanson et al. 1970).
Deoxyneocryptotanshinone (5) is a para-quinone abitanne diterpenod with cytotoxic activity which was isolated from S. miltiorrhiza for the first time (Ikeshiro et al. 1991).
Microstegiol (7) is a rearranged abietane with a sevenmember ring skeleton. This compound has solely been reported from Salvia genus so far (Topcu et al. 2013;Ulubelen et al. 1992). It has been shown to have mild antibacterial effects (Topçu and Gören 2007).

Plant material
The roots of Salvia rhytidea were collected from Taftan Mountain, 28°36′ N and 61°4′ E, in the Baluchistan of Iran at an altitude of 2497 m, in autumn 2012. The plant was authenticated by Dr. Valizadeh and a voucher specimen (no. 4938) was deposited in the Herbarium of the School of Biology (Dr. Akhani Herbarium), University of Tehran.

Conclusions
Our results showed that the root of S. rhytidea contained different types of abietane and rearranged abietane diterpenoids. Biological properties of some of these compounds have been reported previously. Accordingly, S. rhytidea could be considered as a new and rich source of natural agents for the treatment of cancer, malaria, and microbial strains.