THE BIOSYNTHESIS OF TROPIC ACID .3. COMPETITIVE FEEDING EXPERIMENTS WITH TROPIC ACID PRECURSORS IN DATURA

Phenyl{1-C-14]alanine[3],phenyl[2-C-14]pyruvate[4], and phenyl[1-C-14]lactate [5] were fed singly and in competition with unlabeled phenylalanine, phenyllactate, and phenylpyruvate to Datura stramonium. The activities recorded in the alkaloids hyoscyamine [1] and hyoscine (scopolamine) [2] suggested that phenyllactate [5] was the closest precursor for the tropic acid moiety of these alkaloids. Hyoscyamine[1], from plants fed with phenyl[2-C-14]pyruvate [4], was hydrolyzed, but the resultant tropic acid 7 contained only 21% of the activity, the remainder being located in the tropine. However, degradation of the tropic acid showed that the phenylpyruvate incorporated in a specific manner, although it is clearly not an efficient precursor.