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).