THE INCORPORATION OF 3-HYDROXY-3-METHYLGLUTARIC ACID INTO THE LACTONE RING OF DIOSCORINE IN DIOSCOREA HISPIDA

Article abstract of DOI:10.1016/0031-9422(89)80340-1

<3-(14)C>- and <3,3'-(13)C2,3-(14)C>-3-Hydroxy-3-methylglutaric acid were administered to Dioscorea hispida plants, resulting in formation of labelled dioscorine (0.2 percent absolute incorporation).A chemical degradation indicated that there was a non-random incorporation of (14)C into the lactone ring of the alkaloid, the major part of the radioactivity being at its C-10 position.This specific labelling was confirmed by examination of the 13C NMR spectrum of the enriched dioscorine derived from the (13)C2-labelled precursor.There was some scrambling of label, presumably due to catabolism of the 3-hydroxy-3-methylglutaric acid to acetyl-coenzyme A followed by recycling of this intermediate.However the most significant satellites in the 13C NMR spectrum were those arising from contiguous (13)C atoms at C-10 and C-13 of the dioscorine.Ethyl <6-(14)C> orcellinate failed to serve as a significant precursor of dioscorine.These results indicate that 3-hydroxy-3-methylglutaric acid, or more likely its mono coenzyme A ester, is an intermediate between acetate and the branched eight-carbon unit required for the biosynthesis of dioscorine.Key Word Index - Dioscorea hispida; Dioscoreaceae; dioscorine; alkaloid biosynthesis; 3-hydroxy-3-methylglutaric acid; 13C NMR spectroscopy.