Of 3-arylisoquinoline alkaloids

The small group of 3-arylisoquinoline alkaloids are biogenetically related to benzo[c]phenanthridine alkaloids (113). Corydamine (266) was synthesized from (+ )-tetrahydrocoptisine (82) through C-6—N bond cleavage using the von Braun reaction followed by aminolysis and dehydrogenation (Scheme 46) (142). 

Scheme 46. Synthesis of 3-arylisoquinoline alkaloids. Reagents a, BrCN b, CH3NH2 c, 10% KOH, EtOH d, Pd, tetralin e, NaBH3CN f, T1(N03)3, MeOH g, 5% HC1 h, H2CrOA, H2SO i, CH2N2.

The 6,7-secoberbine alkaloids contain the four following natural products corydalic acid methyl ester (55), corydamine (56), N-formylcorydamine (57), and hypecumine (58). These bases, called 3-arylisoquinolines, were described by Shamma and Moniot (2) as a separate class of isoquinoline alkaloids. Santavy (7) classified them among benzophenanthridines. It seems, however, that they may be considered as biosynthetic intermediates between the protoberberines on the one hand and the benzophenanthridines on the other. 

In this small group of alkaloids, the 3-arylisoquinolines, as in the benzo-phenanthridines (see Sec. 21.1) to which they are clearly related, the nitrogen heterocycle can be either fully aromatic or saturated. All three members of the 3-arylisoquinolines have been isolated from Corydalis incisa, a plant also known to produce benzophenanthridines. 

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