Figure 3: biosynthesis of atropine
Synthesis of N-methyl-14C-tropine and N-methyl-14C-atropine.
Tropane Alkaloid and Nicotine Biosynthesis
The biosynthesis of Atropine starting from L-Phenyalanine first undergoes a transamination forming Phenypyruvic Acid which is then reduced to Phenyl-lactic Acid. Coenzyme A then couples Phenyl-Lactic Acid with Tropine forming Littorine, which then undergoes a radical rearrangement initiated with a enzime forming Hyoscyamine Aldehyde. A dehydrogenase then reduces the aldehyde to a primary alcohol making Hyoscyamine, which upon racemization forms atropine.
The effects of antidotal therapy on neuronal RNA content have been studied by Doebler et al. (1983). Soman produced a virtually complete inhibition of acetylcholinesterase activity and moderate decline in neuronal RNA content. Atropine pre-treatment together with pralidoxime reduced RNA levels but increased acetylcholinesterase activity. Thus, no precise relationship exists between the restoration of neuronal acetylcholinesterase (AChE) and AChE activity. The effects on neuronal RNA metabolism may, rather, reflect alterations in acetylcholine sensitivity; if this is so, then manipulation of acetylcholine responsiveness may be a further mechanism for therapeutic intervention. Sterling et al. (1988) studied two drugs found to inhibit presynaptic acetylcholine synthesis in vitro. In a rat model, pre-treatment with N-hydroxyethylnapthylvinylypyridine (NHENVP) or N-allyl-3 quinuclidinol was found to protect rats from soman toxicity, enhancing the effects of atropine and pralidoxime.
Tropinone is located at a branch point in tropane alkaloid synthesis
Thus the effects of atropine, pralidoxime and other drugs that synergistically decrease organophosphate toxicity are complex and as yet, not elucidated fully. Although there are promising new therapeutic approaches, the clinical usefulness of clonidine, calcium channel blockers and presynaptic blockade of acetylcholine synthesis is not yet known.
The alkaloid, atropine, is an organic ester which may be prepared synthetically by combining tropine and tropic acid (McEvoy 2002), but is usually obtained by extraction from some solanaceous plants (Parfitt,1999).
biosynthesis of tropine and chemical synthesis of atropine.
Hereafter the biosynthesis pathway:
I. L-phenylalanine is transaminated to phenylpyruvic acid and then reduced to phenyl-lactic acid
putrescine-N-methyltransferase catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to an amino group of putrescine, which is the first committed step in the biosynthesis of nicotine and tropane alkaloids. This enzyme is expressed in tobacco plant such as in Atropa belladonna because first steps of nicotine biosynthesis, obtained from tobacco plant, are the same of atropine biosynthesis. N-methyl-putrescine is then converted to tropinone, whose keto group is in turn converted by the tropinone reductase-I to the alpha-hydroxyl of tropine
phenyl-lactic acid binds to coenzyme A and reacts with tropine to form littorine, that go through a radical transposition to make hyoscyamine aldehyde. At last, a dehydrogenase reduces the aldehyde to alcool forming hyoscyamine
is also possible to obtain atropine through a chemical synthesis. This process, first discovered by Richard Willstater, is based on the reaction of tropine with tropic acid while in the presence of hydrochloric acid
Synthesis of tropine-labeled atropine
Amino alcohols contain both an amine and an alcohol group
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Atropine - Wikipedia
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