THE BIOSYNTHESIS OF TROPANE ALKALOIDS IN DATURA-STRAMONIUM - THE IDENTITY OF THE INTERMEDIATES BETWEEN N-METHYLPYRROLINIUM SALT AND TROPINONE

The biosynthesis of the tropane alkaloids in transformed root cultures of Datura stramonium has been studied using sodium [1,2-C-13(2)]aceta te, -C-13(2)]-1-(1-methyl-2-pyrrolidinyl)propane-2-one {(R,S)-[2',3'-C -13(2)]hygrine}, ethyl -13(2),2-C-14]-2-(1-methyl-2-pyrrolidinyl)aceta te, and ethyl -C-14]-4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoate. The i ncorporation of (R,S)-[2',3'-C-13(2)]hygrine into cuscohygrine and sev eral other condensation products was high (15-40% specific incorporati on), but label was not recovered in either tropine or tropine esters ( hyoscyamine; 0.0 +/- 0.5% specific incorporation). None of the recover ed alkaloids was labeled when ethyl (R,S) C-13(2),2-C-14]-2-(1-methyl- 2-pyrrolidinyl)acetate was fed to the cultures. In contrast, sodium [1 ,2-C-13(2)]acetate and ethyl 3-C-14]-4-(1-methyl-2-pyrrolidinyl)-3-oxo butanoate were incorporated into hyoscyamine (9 and 2% specific incorp oration, respectively) and a number of other tropane alkaloids (up to 12% specific incorporation). These data provide further evidence that hygrine is not a direct precursor of tropane alkaloids. C-13-Label fro m acetate was incorporated symmetrically into the C-2 and C-4 position s of(-)-hyoscyamine, The evidence supports a pathway in which acetoace tate reacts via its C-4 position with N-methyl-Delta(1)-pyrrolinium sa lt to give 4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoate. This intermedia te favors cyclization to give 2-carboxytropinone, tropinone being form ed by decarboxylation.