Abstract. (S)-(-)-Tropic acid is the acidic moiety of the tropane ester alkaloids, hyoscyamine and scopolamine (hyoscine). When tropic acid is fed to transformed root cultures of Datura stramonium L. or a Brugmansia (Datura) candida • B. aurea hybrid, the formation of these alkaloids is inhibited. Phenyllactic acid, from which the tropoyl moiety is derived, is considerably less inhibitory. Label from (RS)-phenyl[1,3-13Cjlactic acid is incorporated at high levels into apoatropine, littorine, aposcopolamine, hyoscyamine, 713-hydroxyapoatropine, scopolamine and 713-hydroxyhyoscyamine when fed to these cultures. The presence of an excess concentration of unlabelled tropic acid has little influence on the specific incorporation into these products. It is concluded that free tropic acid is not an intermediate in hyoscyamine biosynthesis but rather that the rearrangement of phenyllactic acid occurs subsequent to its esterification.

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Euphorbia serrata latex has initially ingenol-3-palmitate, which by action of silica gel is converted to ingenol-20-palmitate. The former is responsible for the irritant and cocarcinogenic activity of the latex on mouse ear and on mice back skin.

Phenyl{ 1 -14C]alanine [31, phenyl[2-14C)pyruvate [4], and phenyl[ 1 -14C]lactate [51 were fed singly and in competition with unlabeled phenylalanine, phenyllactate, and phenylpyruvate to Datura stramonium. The activities recorded in the alkaloids hyoscyamine [11 and hyoscine (scopolamine) [21 suggested that phenyllactate [51 was the closest precursor for the tropic acid moiety of these alkaloids.Hyoscyamine [11, from plants fed with phenyl[2-14C}pyruvate [4l, 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.( -)-S-Tropic acid is the aromatic acid moiety of the important tropane ester alkaloids hyoscyamine [1] and hyoscine (scopolamine) (2], which are constituents of Datura spp. Its biosynthesis, which has aroused much interest, was first investigated in I960 when Leete (1) demonstrated that the label from phenyl[3-14C]alanine infiltrated into Datura stramoniumL. (Solanaceae) incorporated into C-2 of tropic acid [6], Underhill and Youngken (2) and Gross and Schutte (3) were able to confirm this result using intact D. stramonium and Datura metel isolated root cultures, respectively. The former workers reported that phenylacetic acid was also a good precursor but that the usual one-carbon sources (formate and serine), capable of extending the two-carbon side chain to three carbons, only labeled the tropane part of the ester alkaloids. Methionine and formaldehyde (1) also failed as additional one-carbon sources, but bicarbonate (4), although labeling other carbons, predominantly labeled the hydroxymethyl group of tropic acid, a result that favored the intermediacy of phenylacetate. However, it was later (5) demonstrated that all three carbons in the side chain of tropic acid [6} were derived from the side-chain carbons of phenylalanine [31 by means of a rearrangement (Scheme 1). The primary role of phenylalanine was confirmed when it was shown that after very careful purification, the alkaloids derived from phenylacetate feedings were devoid of activity 'Part 3 in the series "The Biosynthesis of Tropic Acid.' For Part 2, see Evans and Woolley ( 14). 2Dedicated to the memory of Professor Edward Leete.