The biosynthetic pathways for the tropane alkaloids have been studied in considerable detail and are associated with nicotine biosynthesis,since the N-methyl-D1-pyrrolinium cation is a precursor to both classes of alkaloids.
The formation of the tropane nucleus from ornithine and acetoacetate was first investigated in plants using radioactive tracers aslong ago as 1954, but it was not until the early
1980s that a biosynthetic scheme was finally elucidated in Erythroxylon coca.The pathway for biosynthesis of hyoscyamine and scopolaminc is quite complex, since not only is an acetone unit required for the formation of tropinol (19), but a second converging pathway is necessary for the conversion of phenylalanine to tropic acid . Recent work with root cultures of Datura stramonium, suggests that hygrine is not an intermediate, but an off shoot from the main pathway .The biosynthesis of cocaine is similar to that of hyoscyamine .The N-methylation
and cyclization of ornithine-derived putrescine gives the N-methyl-D1-pyrrolinium cation, which condenses with acetoacetyl- CoA.Methylation of the free carboxylate group followed by ring closure, reduction of the ketone group, and benzoylation results in the formation of cocaine.The benzoic acid is derived from phenylalanine.The molecular biology of tropane alkaloid synthesis is being studied extensively and holds considerable potential for alkaloid biotransformations.An elegant example is the construction of a transgenic species of Atropa belladonna that was able to accumulate theimportant pharmaceutical scopolamine instead of hyoscyamine.
The formation of the tropane nucleus from ornithine and acetoacetate was first investigated in plants using radioactive tracers aslong ago as 1954, but it was not until the early
1980s that a biosynthetic scheme was finally elucidated in Erythroxylon coca.The pathway for biosynthesis of hyoscyamine and scopolaminc is quite complex, since not only is an acetone unit required for the formation of tropinol (19), but a second converging pathway is necessary for the conversion of phenylalanine to tropic acid . Recent work with root cultures of Datura stramonium, suggests that hygrine is not an intermediate, but an off shoot from the main pathway .The biosynthesis of cocaine is similar to that of hyoscyamine .The N-methylation
and cyclization of ornithine-derived putrescine gives the N-methyl-D1-pyrrolinium cation, which condenses with acetoacetyl- CoA.Methylation of the free carboxylate group followed by ring closure, reduction of the ketone group, and benzoylation results in the formation of cocaine.The benzoic acid is derived from phenylalanine.The molecular biology of tropane alkaloid synthesis is being studied extensively and holds considerable potential for alkaloid biotransformations.An elegant example is the construction of a transgenic species of Atropa belladonna that was able to accumulate theimportant pharmaceutical scopolamine instead of hyoscyamine.
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