Structure of three new terpenoids, spiciformisins a and b, and monocyclosqualene, isolated from the herbs of Ligularia fischeri var. spiciformis and cytotoxicity

The diethylet-er fraction from the leaves extract of Ligularia fischeri var. spiciformis (Compositae) was subjected to silica gel column chromatography and yielded three new terpenoids named spiciformisin a (1), spiciformisin b (3), and monocyclosqualene (2). Acyclic diterpenes, spiciformisin a and -b, were established as 3,7,11,15-tetramethyl-1,3(20)-hexadecadiene and 3,7,11,15-tetramethyl-1,3,6,10,14-hexadecapentaene (IUPAC), respectively. A monocyclic triterpene, monocyclosqualene, were determined as [3,8,12,16,16-pentamethyl-(3,7,11,15-hexadecatetraenyl)]-3,3,5-trimethyl-1-cyclohexene. The structures were determined on the basis of NMR and MS analysis. Spiciformicin b showed potent cytotoxicity (IC50, <9.7 mug/ml against HL-60) in contrast to no cytotoxicity (IC50, >200 mug/ml against HL-60 cells) of spiciformicin a with a cis-conjugated dienyl diexomethylene.