BIOSYNTHESIS OF SECOIRIDOID GLUCOSIDES IN OLEACEAE

The biosynthesis of the oleoside-type of glucosides (oleosides) has be en investigated in two species of Oleaceac, namely Fraxinus excelsior and Syringa josikaea. Deuterated analogues of deoxyloganic acid, 8-epi -deoxyloganic acid, 7-epi-loganic acid and loganic acid were prepared. On administration of the above compounds high incorporations of deoxy loganic acid as well as of loganic acid and its 7-epimer were obtained , strongly implying that 7-ketologanic acid is an intermediate in the biosynthesis of oleosides. The incorporations were measured by H-2 NMR in several isolated secoiridoids all belonging to the oleosides. In a ddition, the content of acidic iridoids (both carbocyclic and seco-typ e) in two additional species of Oleaceae, namely Ligustrum ovalifolium and Phillyrea latifolia, were examined. Based on these results, a pla usible biosynthetic route from deoxyloganic acid, 7-epi-loganic acid, 7-ketologanic acid, 8-epi-kingisidic acid, oleoside 11-methyl ester, 7 -beta-1-D-glucopyranosyl 11-methyl oleoside and ligstroside to oleurop ein can now be presented.