Isolation of the major component in white snakeroot that is toxic after microsomal activation: possible explanation of sporadic toxicity of white snakeroot plants and extracts.

Tremetone, the major toxic component in white snakeroot (Eupatorium rugosum Houtt) extracts, was isolated following an in vitro bioactivity assay. Microsomal activation was required to produce a product toxic to murine melanoma (B16F1) cells as well as five other mammalian cell cultures. The metabolic activation product(s) of tremetone is suspected to be responsible for the toxic activity of the plant. Tremetone is also smoothly converted to dehydrotremetone in the plant and cell free homogenates, and readily decomposes to dehydrotremetone in extracts. Dehydrotremetone is not toxic even after microsomal activation. The efficient conversion of tremetone to dehydrotremetone may explain why white snakeroot plant material and extracts have varied activities, and why a previous claim that tremetone was responsible for the toxic activity of white snakeroot was withdrawn. Rayless goldenrod extracts show the same toxic activity as white snakeroot and the toxic activity of rayless goldenrod is most likely due to tremetone.