BIOSYNTHESIS OF THE IRIDOID GLUCOSIDE CORNIN IN VERBENA OFFICINALIS

Article abstract of DOI:10.1016/0031-9422(89)85017-4

The biosynthesis of cornin (verbenalin) and dihydrocornin in Verbena officinalis has been investigated.The incorporation of <2H> deoxyloganin was found to be largely independent of the incubation time between one day and a week.An improved method for the preparation of deoxygeniposide from gardenoside is reported and <2H>-iridodial glucoside and iridotrial glucoside were prepared from the former.Feeding experiments with young plants using these glucosides, as well as the aglucones, showed much better incorporations for the latter compounds as measured by 2H NMR spectroscopy. 13C-labelled 10-hydroxygeraniol, 10-hydroxycitronellol, iridodial, iridotrial, iridodial glucoside, iridotrial glucoside, deoxyloganic acid aglucone were prepared. <13C>-Mevalonic acid and the above compounds were fed to plants of medium age, and all gave incorporations measurable by 13C NMR spectroscopy into dihydrocornin.The postulated existence of two different metabolic pathways in the biosynthesis of cornin in young and old plants, respectively, could not be established as complete scrambling between the C-3 and C-11 in the iridoid skeleton apparently takes place with all the early precursors.The complete pathway from iridoidal forwards to hastatoside has been elucidated.Key Word Index- Verbena officinalis; Verbenaceae; cornin; dihydrocornin; iridoid glucosides; biosynthesis; 13C-labelling; 2H-labelling.