Toxicity of sesquiterpene lactones

The intraperitoneal LD50 of 7 sesquiterpene lactones were determined (in mg/kg): mexicanin-E (3, 3.08 +/- .10), helenalin (1, 9.86 +/- .08), hymenoxon (2, 16.24 +/- .10), psilotropin (4, 112.25 +/- .17), hymenoxon dimethyl ether (5, 141.42 +/- 0), tenulin (6, 184.65 +/- .06), and hymenolane (7, above 200). The toxicity of a sesquiterpene lactone depends on the number of alkylating centers such as cyclopentenone, alpha-methylene-gamma-lactone, or hemiacetal moieties in the molecules.