The first drugs used in treating parkinsonism were the alkaloids, atropine and scopo-lamine, and over the course of many years they were the only drugs used for this purpose. However, in treating Parkinsonism today, these alkaloids are used extremely rarely and have been practically replaced by synthetic drugs that exhibit central anticholinergic properties (central cholinoblockers). They suppress stimulatory cholinergic effects by suppressing cholinoreceptors. It is believed that they do not affect the synthesis, release, or hydrolysis of acetylcholine. Their action facilitates the reduction or alleviation of motor disturbances associated with damage to the extrapyramidal system. They reduce rigidity and to a lesser extent akinesia, and have a minimal effect on tremors. The therapeutic value of such drugs is relatively small and they are used either in combination with levodopa, or in cases of minor Parkinsonism, primarily for alleviating rigidity. In addition, they cause a number of side effects, including general weakness, headaches, and so on.
Trihexyphenidyl: Trihexyphenidyl, 1-cyclohexyl-1-phenyl-3-piperidineopropan-1-ol (10.2.2), is synthesized by the reaction of 2-(1-piperidino)propiophenone (10.2.1) with cyclo-hexylmagnesiumbromide. The initial 2-(1-piperidino)propiophenone is synthesized in turn by the aminomethylation of benzophenone using paraformaldehyde and piperidine [24-27].
Trihexyphenidyl, an antiparkinsonian drug, possesses central and peripheral anticholinergic actions, as well as a direct relaxant effect on smooth muscle. It reduces muscle rigidity and general stiffness, and has a relatively minor effect on tremors. It is used in Parkinsonism in the form of monotherapy as well as in combination with levodopa. The most common synonyms are parkopan, parkinsan, and cyclodol.
Procyclidine: Procyclidine, 1-cyclohexyl-1-phenyl-3-pirrolidinopropan-1-ol (10.2.3), is synthesized in the exact same manner, except beginning with 2-(1-pyrrolidino) propio-phenone [28-32].
In terms of pharmacological properties, it basically does not differ from trihexyphenidyl. The most common synonym of procyclidine is cemadrin.
Biperiden: Biperiden, 1-(5-norbornen-2-yl)-1-phenyl-3-piperidinopropan-1-ol (10.2.4), is also synthesized according to the method of making trihexyphenidyl, except by reacting 2-(1-piperidino)propiophenone (10.2.1) with 5-norbornen-2-ylmagnesiumbromide [33,34].
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