(organic chemistry) A psoralen chemical compound containing (-)-marmesin linked to beta-D-glucosyl residue, found in some plants. (2S)-2-[2-[(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxypropan-2-yl]-2,3-dihydrofuro[3,2-g]chromen-7-one