Coupling reactions of secologanin

Reinvestigation and completion of the coupling reaction of secologanin with biogenic amines... 

Fig. (11). Coupling reaction of secologanin with tryptamine and oxotryptamine.

Next, the coupling reaction of tetraacetylsecologanin (7) with 2-oxo-2,3-dihydrotryptamine (76a) (in the following oxotryptamine) and its Nb-benzyl derivative (76b) was studied according to Fig. (11). Previously, Brown and co-workers investigated the reaction with secologanin... 

The biochemical importance of secologanin is indicated by the fact that the coupling reaction with tryptamine and dopamine is the first step in the biosynthesis of about 2500 indole, isoquinoline and related alkaloids [2, 7], the most typical of which are shown in Fig. (2). 

Based on knowledge of a biosynthetic pathway one can select certain steps which could be of interest for bioconversion of (a) readily available precursor(s). This could, for example, be stereospecific reactions, like the reduction of quinidinone in quinine or quinidine and the epoxidation of atropine to scopolamine. For the bioconversion one can consider using plant cells [e.g., the production of L-dopa from tyrosine by immobilized cells of Mucuna pruriens (10)] or isolated enzymes from the plant itself. An interesting example of the latter is the (5)-tetrahydroprotoberberine oxidase (STOX) enzyme, which oxidizes (5)-reticuline but not its stereoisomer (11). This feature can be used in the production of (i )-reticuline from a racemic mixture (see below). Immobilized strictosidine synthase has been successfully used to couple secologanin and tryptamine. The gene for this enzyme has been isolated from Rauvolfia (6) and cloned in Escherichia coli, in which it is expressed, resulting in the biosynthesis of active enzyme (7). The cultured bacteria produced 20 times more enzyme... 

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