The biosynthesis of tropic acid in plants: evidence for the direct rearrangement of 3-phenyllactate to tropate

Abstract

Dual labelled sodium (RS)-3-phenyl[2-¹³C, 2-²H]lactate was incubated with transformed root cultures of Datura stramonium and the incorporation of the label into the tropic acid ester moiety of hyoscyamine was assessed by ¹³C{¹H} and ¹³C{¹H,²H} NMR spectroscopy and by GC–MS analysis. It is demonstrated that the ¹³C–²H bond of sodium (RS)-3-phenyl[2-¹³C,2-²H]lactate is incorporated (GC–MS, M + 2, 17%) intact into the hydroxymethyl group at C-3′ of the (S)-tropoyl moiety. This result demonstrates unambiguously that 3-phenyllactate is a closer precursor to the tropate ester than phenylpyruvate or phenylalanine.