The biosynthesis of cocaine, hyoscyamine and related tropane alkaloids will be studied by administering putative precursors, labeled with isotopes (13C,14C,2H,3H,15N) to intact plants, root cultures, or incubating these compounds with cell-free systems. The cell-free systems will hopefully yield enzymes which catalyze individual steps in the biosynthesis of these medically important drugs (hyoscyamine - the (S)-form of the racemic alkaloid atropine, scopolamine - widely used as a post-operative anti- nausea drug). Although cocaine is used medically as a local anesthetic, the focus of this proposal is to learn as much as possible about the way in which cocaine is synthesized in the Erthroxylum coca plant. Root cultures of E. coca will be established to determine whether any cocaine or related tropane alkaloids are synthesized in the roots of this species. Since no enzymes have been so far isolated from E. coca, which catalyze any of the steps of cocaine biosynthesis, an attempt will be made to isolate some of these from this plant. Attempts will be made to inhibit the formation of cocaine in the leaves of the coca plant by administering compounds which are known to inhibit the enzymes which are hypothetically though to be involved in the biosynthesis of cocaine (e.g. alpha-difluoromethyl ornithine which is an inhibitor or ornithine decarboxylase). There are several significant gaps in our knowledge of the pathway between ornithine and the ultimate hyoscyamine and scopolamine. This pathway has been investigated much more than the one ultimate hyoscyamine and scopolamine. This pathway has been investigated much more than the one leading to cocaine. There will be a collaboration with two groups (Professor Y. Yamada, at Kyoto University Japan, and Dr. R.J. Robins at the Institute for Food Research, Norwich, UK) who have made important contributions to current knowledge on the biosynthesis of the tropane alkaloids. The plausibility of some of the proposed steps in biosynthesis of the tropane alkaloids will be examined by studying the biomimetic conversion of proposed biosynthetic intermediates, or closely related compounds, to compound which are considered to be more advanced intermediates in the biosynthesis of the alkaloids. Determination of the biosynthesis of these tropane alkaloids, and the level of the various enzymes in the biosynthetic pathway may yield information on the flux of intermediates though the pathway. This knowledge could lead to the production of modified biological systems which would afford higher yields of desireable alkaloids, than are currently only available from field grown plants. Information gained on the biosynthesis of cocaine could lead to methods, perhaps involving molecular biology, by which the biosynthesis of cocaine in the Erythroxylum coca plant could be inhibited.
|Leete, E (1990) Recent developments in the biosynthesis of the tropane alkaloids. Planta Med 56:339-52|
|Leete, E (1987) 2,3-Dehydrococaine: not a direct precursor of cocaine in Erythroxylum coca. J Nat Prod 50:30-5|
|Leete, E; Rana, J (1986) Synthesis of [3,5-14C]trachelanthamidine and [5-3H]isoretronecanol and their incorporation into the retronecine moiety of riddelliine in Senecio riddellii. J Nat Prod 49:838-44|