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

The diethylether 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 microg/ml against HL-60) in contrast to no cytotoxicity (IC50, >200 microg/ml against HL-60 cells) of spiciformicin a with a cis-conjugated dienyl diexomethylene.