Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2010
Publication Date: 7/6/2010
Publication URL: http://dx.doi.org/10.1016/j.phytochem.2010.06.003
Citation: Cool, L.G., Vermillion, K., Takeoka, G.R., Wong, R.Y. 2010. Irregular sesquiterpenoids from Ligusticum grayi roots. Phytochemistry. 71 (2010), pp. 1545–1557 doi:10.1016/j.phytochem.2010.06.003. Interpretive Summary: Ligusticum grayi J.M. Coult. & Rose (oshala, Gray’s lovage, Gray’s wild lovage, Gray’s licorice root) is a perennial herb that grows in the Sierra Nevada, Klamath, and Cascade Mountains of California, Nevada, Oregon, and Washington and in similar habitats in Idaho, Montana and westernmost Utah. Roots of this species and the more easterly L. porteri “osha” were valued by Native Americans for medicinal purposes and were used to treat colds, coughs, stomachaches. Herbalists currently use the root for similar medicinal treatments and the herb is reported to have anti-bacterial and possibly anti-viral properties. The aromatic roots have a pleasant and distinctive odor. In our continuing efforts to identify biologically active constituents in natural products we studied the chemical composition of L. grayi roots. We identified a total of 41 constituents including 18 sesquiterpenoids which were identified for the first time in nature. We plan to study the biological activity of these 18 newly characterized constituents.
Technical Abstract: Root oil of Ligusticum grayi (Apiaceae) contains numerous irregular sesquiterpenoids. In addition to the known acyclic sesquilavandulol and a new sesquilavandulyl aldehyde, two thapsanes, one epithapsane, and fourteen sesquiterpenoids representing eight novel carbon skeletons were found. The new skeletons are: prethapsane, i.e. 1,1,2,3a,7,7-hexamethyloctahydro-1H-indene; isothapsane, i.e. 1,2,3a,6,7,7a-hexamethyloctahydro-1H-indene; ligustigrane, i.e. 1,1,2,7,7,7a-hexamethyloctahydro-1H-indene; isoligustigrane, i.e. 1,1,2,6,7,7a-hexamethyloctahydro-1H-indene; preisothapsane, i.e. 1,1,2,3a,6,7-hexamethyloctahydro-1H-indene; isoprethapsane, i.e. 1,1,2,4,7,7-hexamethyloctahydro-1H-indene; allothapsane, i.e. 1,1,2,3a,7,7a-hexamethyloctahydro-1H-indene; and oshalagrane, i.e. 1,1,2,4,6,6-hexamethylspiro[4.4]nonane. The bicyclic sesquiterpenoids are presumably biosynthesized by head-to-head coupling of geranyl diphosphate and dimethylallyl diphosphate, followed by a cyclization sequence leading to a hydroindane skeleton with six one-carbon substituents. Subsequent rearrangements—primarily methyl migrations—account for the remarkable variety of structures represented in L. grayi root oil.