BIOSYNTHESIS OF MUSTARD OIL GLUCOSIDES: VI. BIOSYNTHESIS OF GLUCOBARBARIN IN RESEDA LUTEOLA L.

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Abstract
A number of C14-labelled compounds were fed to Reseda luteola L.; after a 24-hour period of metabolism, the thioglucoside aglycone (5-phenyl-2-oxazolidinethione) was isolated and its specific activity determined. In some instances the aglycone was degraded to determine the distribution of C14.DL-γ-Phenylbutyrine (2-amino-4-phenylbutyric acid) was the most efficient precursor of the aglycone, followed by phenylalanine and acetate; the carboxyl carbon of these compounds was not incorporated into the thioglucoside aglycone. Little or no randomization of C14 in the aglycone resulted from feeding DL-γ-phenylbutyrine-2- and -3-C14, DL-phenylalanine-2- and -3-C14, and acetate-2-C14. The conversion of C14 from 10 additional compounds into the aglycone was less than that from D-glucose-G-C14. Isotope competition experiments suggest that β-benzylmalic acid also may be a precursor. It appears that the C6–C3 aglycone is formed from phenylalanine and acetate via C6–C5 and C6–C4 intermediates (including γ-phenylbutyrine or its keto acid analogue) in a manner analogous to the formation of gluconasturtiin in watercress. The carbon-14 and nitrogen-15 of L-phenylalanine-G-C14-N15 and of DL-γ-phenylbutyrine-2-C14-N15 were not incorporated as a unit into the aglycone of glucobarbarin.