THE BIOSYNTHESIS OF TROPIC ACID IN PLANTS - EVIDENCE FOR THE DIRECT REARRANGEMENT OF 3-PHENYLLACTATE TO TROPATE

Dual labelled sodium (RS)-3-phenyl[2-C-13,2-H-2]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 C-13{H-1} and C-13{H-1,H-2} NMR spectroscopy and by GC-MS analysis. It is demonstrated that the C-13-H-2 bond of sodium (RS)-3-phenyl[2-C-13,2-H-2]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.