Pictet-Spengler condensation mechanism

The Pictet-Spengler condensation of indole bases and carbonyl compounds to form 3-carbolines involves a slightly different mechanism than the isoquinoline... 

Tryptophan-derived 1,2,3,4-tetrahydro-P-carboline and 3-carboline alkaloids result in foods through a Pictet-Spengler condensation (a special case of the Mannich reaction) of indoleamines, such as tryptophan and tryptamine, with aldehydes. The mechanism of the Pictet-Spengler reaction leading to... 

NCS catalyzes isoquinoline formation via an asymmetric Pictet-Spengler reaction (ii). The reaction entails an acid-catalyzed electrophilic addition of an iminium ion. The mechanism is a two-step process in which the iminium ion is generated first from the condensation reaction between the aldehyde carbonyl (such as 4-HPAA) and dopamine. Two types of NCS (CjNCSl and CjPRlOA) have been isolated from Coptis japonica cells and characterized [21]. CjPRlOA has been sufficiently expressed in an active form in E. coli. Conversely, CjNCSl forms a larger complex in plant cells. Therefore, the recombinant enzyme expressed in E. coli cells has considerably lower activity than that of the native enzyme. 

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