Ruta Umbelliferone

The enzyme that catalyses the conversion of DMAPP and umbelliferone into 6-dimethylallylumbelliferone, the first reaction specifically directed to the biosynthesis of linear furanocoumarins, has been isolated394 from suspension cultures and young leaves of Ruta graveolens. The particulate enzyme could utilize neither herniarin as a substitute for umbelliferone nor GPP in place of DMAPP. 8-Dimethylallylumbelliferone, which is an intermediate in the formation of the angular furanocoumarins, was not formed by these preparations. 

Umbelliferone is the pivotal metabolite in the pathways to substituted coumarins and furano- or pyranocoumarins. Its 7-0-methylation to herniarin (Fig. 4.3) or 0-prenylation and C-alkylation reactions are often observed in coumarin-producing higher plants where the prenylation at C-6 or C-8 mark the entry to the routes branching linear from angular furano- and pyranocoumarins (Fig. 4.5). In Ruta graveolens and Ammi rmjus, the prenylation reactions are catalysed by particulate enzymes (Hamerski et at, 1990), and... 

Information on the origin of angular furanocoumarins has not been plentiful, but much more is known about the more widely distributed linear isomers. In brief, the committed step in the pathway is the condensation of mevalonate-derived dimethylallyl pyrophosphate (DMAPP) at position 6 of umbelliferone to yield 7-dimethylsuberosin (Scheme 5). A transferase mediating this step was identified and characterized in Ruta graveolens 3 o 3 d evidence was obtained that it is a chloroplast enzyme.Cyclization... 

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