New isoprenoids with rare scaffolds from Salvia hydrangea

The genus Salvia (Lamiaceae) is a rich source of structurally diverse isoprenoids. As part of a project aimed at the discovery of structurally new bioactive metabolites from Iranian Lamiaceae, we studied Salvia hydrangea, a species commonly known in Persian as “Gol-e Arooneh”. The flowers of S. hydrangea are used in popular Iranian medicine as an anthelmintic and antileishmanial drug. We previously identified several new antiplasmodial isoprenoids from this species [1,2]. A further phytochemical investigation of the aerial parts of S. hydrangea was conducted to identify minor isoprenoids. Fractionation of the n-hexane extract by a combination of open column chromatography on silica gel and preparative and semi-preparative RP-HPLC afforded five new isoprenoids. Their structures were established on the basis of extensive spectroscopic analysis, including MS, 1D and 2D NMR, and X-ray crystallographic analysis and ECD for determination of absolute configurations. Four compounds, including 1, possess a six membered ring fused at C-8, C-9, and C-24 with other carbocycles of the scaffold while compound 2 represents a new scaffold bearing a five membered ring instead. These isoprenoids are assumed to result from the cycloaddition of a diterpene with a monoterpene, followed by subsequent steps of oxidation and cyclization, and they have been found so far only in the genera Salvia and Perovskia.

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[1] Farimani MM, Taheri S, Ebrahimi SN, Bahadori MB, Khavasi HR, Zimmermann S, Burn R, Hamburger M. Org Lett 2012; 14: 166 – 169

[2] Farimani MM, Bahadori MB, Taheri S, Ebrahimi SN, Zimmermann S, Burn R, Amin GR, Hamburger M. J Nat Prod 2011; 74: 2200 – 2205