title: Irregular sesquiterpenoids from Ligusticum grayi roots.
abstract: Root oil of Ligusticum grayi (Apiaceae) contains numerous irregular sesquiterpenoids. In addition to the known acyclic sesquilavandulol and a sesquilavandulyl aldehyde, two thapsanes, one epithapsane, and 14 sesquiterpenoids representing eight hitherto unknown carbon skeletons were found. These 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.
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, 800 Buchanan St., Albany, CA 94710, USA. larry.cool@sbcglobal.net
authors.forename: Laurence G
authors.initials: LG
authors.lastname: Cool
authors.forename: Karl E
authors.initials: KE
authors.lastname: Vermillion
authors.forename: Gary R
authors.initials: GR
authors.lastname: Takeoka
authors.forename: Rosalind Y
authors.initials: RY
authors.lastname: Wong
mesh_terms: D030004:Ligusticum / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D010938:Plant Oils / Q000737:chemistry; D018517:Plant Roots / Q000737:chemistry*; D012717:Sesquiterpenes / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D010938:Plant Oils; D012717:Sesquiterpenes