Synthesis, Reactions and Medicinal Uses of Isoquinoline

Isoquinoline

Synthesis

Bichler – Napieralski synthesis - This reaction involves the formation of an amide from an acylated β-phenylethylamine using an acid-chloride/anhydride. A Lewis acid (phosphoric chloride or pentoxide) can be used to cyclize this amide with a loss of water to give 1-substituted-3, 4-dihydro isoquinoline. Palladium, sulfur, or diphenyl disulfide can readily be used to dehydrate this intermediate to isoquinoline.



Pictet – Gam modification - A cyclization catalyst, POCl3, is used to heat β-hydroxy-β-phenylethylamine in place of β-phenylethylamine.

Pictet-Spengler synthesis - Arylethanamines produce imines when they react with aldehydes. The imine is transformed into 1, 2, 3, and 4 - tetrahydroisoquinoline through acid-catalyzed cyclization. Ring closure (i.e., cyclization) will occur under very mild conditions if electron-donating substituents are present on the phenyl ring. For example,


Ozonolysis of indene - Homophthal-aldehyde is produced when indene is exposed to ozone at –70°C. In the presence of NH4OH, dimethylsulfide is reduced then cyclized with this dialdehyde.

Reactions

Reduction - Under the influence of different reducing agents, isoquinoline produces different reduced products.



Oxidation - Oxidation is difficult for isoquinoline. It undergoes ring cleavage under vigorous conditions, resulting in degradation products.

Medicinal Uses

Dimethisoquin (an anesthetic), debrisoquine, quinapril (an antihypertensive) and papaverine (a vasodilator) are some of these drugs. Berberine, emetine, and other therapeutically active alkaloids are also included.

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