(+/-)-[3,5-14C]Trachelanthamidine and (+/-)-[5-3H]isoretronecanol, which are diastereomers, were prepared from potassium [14C]cyanide and [5-3H]proline, respectively. These compounds and [1,4-14C]putrescine were administered to Senecio riddellii plants resulting in the formation of labeled riddelliine, in which almost all the radioactivity was located in its retronecine moiety. The activity of the beta-alanine obtained by degradation of the retronecine was consistent with specific labeling of this pyrrolizidine base at the expected positions. The extremely high absolute incorporation (15.1, 22.1%) of trachelanthamidine into riddelliine strongly favors this 1-hydroxymethylpyrrolizidine as the one on the main biosynthetic pathway to retronecine. The lower incorporation (0.75%) of isoretronecanol may represent a minor or aberrant pathway to retronecine.

Carbon Radioisotopes↗

PubMedDate not supplied

2,3-Dehydrococaine: not a direct precursor of cocaine in Erythroxylum coca.

(+/-)-3-[4(-3)H]Benzoyloxy-2-[carbonyl-13C, 14C]carbomethoxy-2-tropene (2,3-dehydrococaine) was synthesized from Ba [13C, 14C]CO3 and [4(-3)H]benzoic acid. This labeled compound (3H/14C 0.65) was administered to Erythroxylum coca plants for 3 and 15 days. After these times, cocaine was isolated and was found to have a 3H/14C ratio quite different from the administered dehydrococaine (3.0 and 10.6 for the 3- and 15-day feeding experiments, respectively). Degradations of the cocaine indicated that tritium was all located in the 4-position of its benzoyl moiety. 13C-nmr spectroscopy indicated enrichment of the carbomethoxy group of cocaine, consistent with the observed specific incorporation of the 14C. From the 3-day feeding experiment unmetabolized dehydrococaine was isolated having the same specific activity and 3H/14C ratio as the administered compound. Also from this feeding experiment 2-carbomethoxy-3-tropinone was isolated having about 1/3 the specific activity (14C) of the administered dehydrococaine and having a (-) optical rotation. These results indicate that cocaine is not formed by the direct reduction of dehydrococaine. The results indicate that cocaine is not formed by the direct reduction of dehydrococaine. The results are rationalized by proposing initial hydrolysis of the dehydrococaine to benzoic acid and 2-carbomethoxy-3-tropinone. The latter compound is then reduced to methyl ecgonine, which is then esterified with benzoic acid to yield cocaine. The change in the 3H/14C ratio is due to the fact that only the (+) enantiomer of 2-carbomethoxy-3-tropinone is converted to cocaine, and that different pool sizes of the non-labeled intermediates exist in the plant.

Chemical Phenomena↗