Syntheses of the metabolites from platyphylloside, a phenol causing digestibility inhibition in rumen fluid, have been performed to identify the active metabolite. 1,7-Bis(4‘-hydroxyphenyl)-3-heptanone (3-platyphyllone), racemic, and the two enantiomers of 1,7-bis(4‘-hydroxyphenyl)-3-heptanol (centrolobol) and 1,7-bis(4-hydroxyphenyl)heptane (platyphyllane) were synthesized and tested regarding digestibility inhibition in vitro in cow rumen fluid. All compounds tested induced a decreased digestion. Centrolobol was found to be the metabolite causing the observed effect, and (R)-centrolobol was found to be the enantiomer formed in the rumen liquor in vitro.