Structural Classification of Erythrina Alkaloids

The erythrina-type alkaloids are characterized by their unique tetracyclic spiroamine framework. They are generally classified into two main groups Alkaloids predominantly possessing a 6-5-6-6-membered indoloisoquinoline core are called erythrinanes and those exhibiting a 6-5-7-6-membered indolobenzazepine skeleton are generally called schelhammeranes or homoerythrinane alkaloids (see Fig. 1). 

Depending on the nature of the D ring both groups in turn may be subdivided into aromatic and non-aromatic alkaloids, the latter of which 

Finally, the typical position and the number of olefinic bonds in the A and B ring have led to a further subdivision into dienoids and alkenoids in both alkaloid series. The former are characterized by a conjugated diene unit covering C atoms 1, 2, 6, and 7, while the latter possess only one double bond in the 1,6-position (see Fig. 2). 

The aromatic erythrinanes and homoerythrinanes as the most important members of the Erythrina alkaloids show substimtion patterns of 

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