Atropine and the Tropeines

Atropine was discovered in 1831 in the roots of the belladonna plant, and is a strongly poisonous alkaloid. Its chief use in medicine depends upon its action in dilating the pupil and paralysing the accommodation of the eye, and it is also used to check the inhibition of the heart arising from administration of chloroform and the depressant action of morphine on the respiratory centre. 

Atropine is an ester, and on hydrolysis yields a basic substance, tropine, and optically inactive tropic acid (1). It has been shown that the alkaloid hyoscyamine, which is also obtained from belladonna and is laevo-rotatory, is the ester of tropine with laevo-tropic acid (2), and therefore atropine appears to be racemic hyoscyamine. This view of the nature of atropine has been confirmed by Ladenburg (3), and dextro-hyoscyamine has also been prepared by the union of tropine with dextro tropic acid (4). 

The pharmacology of these three stereo-isomerides, o -hyoscyamine, Z-hyoscyamine, and the racemic form, atropine, has been investigated by Cushny, (5) using the frog as the subject of the experiments. It was found that all three were alike in certain respects, but that with regard to some aspects of their action dextro-hyoscyamine was the strongest and the levo variety the weakest, while with other effects of the drug exactly the reverse was the case. In all cases the action of atropine was intermediate between that of the two optically active forms, and this fact is explained by Cushny by the assumption that atropine is probably decomposed in solution into its two active components. 

As atropine is the ester of tropine with racemic tropic acid, 

Tropic acid is a relatively simple substance, being indeed a homologue of mandelic acid, and having the constitution— 

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The hydroxyl of pseudotropine has been esterified with various aliphatic and aromatic acids. These esters are known as the pseudotropeines. Of these, tiglylpseudotropeine is known under the name tigloidine and has been isolated from Duboisia myoporoides R. Br. (222), while benzoylpseudo-tropeine or tropacocaine has been isolated from the leaves of a species of coca grown in Java (120). Tropacocaine (120) and the pseudotropeines (211), unlike atropine and the tropeines, show no mydriatic properties. 

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