The biosynthesis of tropic acid. Part 6. Enantioselective, intact incorporation of (R)-(+)-3-phenyllactic acid into the tropic acid ester alkaloids of Datura

Abstract

(R)-(+)-11 and (S)-(–)3-Phenyl[1,3-¹³C₂; 1-¹⁴C] lactic acid 13 were fed separately to Datura stramonium(Solanaceae)via the wick method. In a second feeding experiment (R)-(+)- and (S)-(–)-3-phenyl [1,3-¹³C₂; 2-¹⁴C] lactic acid were administered via the roots. In both cases hyoscine (scopolamine) and hyoscyamine 1 and 2, respectively were isolated separately from the roots and aerial parts. The (R)-enantiomer 11 was more efficiently incorporated into the (S)-(–)-tropic acid 8 moiety of both bases. Examination of the ¹³C NMR spectra of the bases and of tropic acid, obtained by hydrolysis of hyoscyamine, showed ¹³C–¹³C spin–spin coupling indicating that the tropoyl ester (–)-hyoscyamine 9 is formed by direct rearrangement of the (R)-(+)-3-phenyllactic acid 11 ester of tropine (littorine).