Comparison of (+)- and (-)-marmesin as intermediates in the biosynthesis of linear furanocoumarins

Marmesin has been identified by chromatography and ultraviolet absorption spectrum in extracts of Ruta graveolens, in confirmation of earlier conclusions from tracer experiments that it is an intermediate in furanocoumarin biosynthesis in this species. Trapping experiments with [2-14C]umbelliferone and (+)- or (−)-marmesin were inconclusive, but indicated that only the (+)-form is metabolically active in R. graveolens. This was confirmed in Ruta and also in Heracleum lanatum and Angelica archangelica by direct comparison feedings of [3-14C](+)- and (−)-marmesin. The (+)-isomer was an efficient furanocoumarin precursor, as before, while little if any utilization of (−)-marmesin could be demonstrated.