Cularine occurrence

Similarities to the aporphine group extend to the occurrence of secocularine (99, R=Me) and secocularidine (99, R=H) in c. claviculata and S. crassifoHa the latter can be methylated to the former, which is identical with the product of Hofmann degradation of cularine methiodide (Boente et al.. Tetrahedron Letters, 1984, 889, 1829 Campello et al, too cit. ). 

To date there have been found only cularine and several of its 0- or N-desmethyl derivatives. The unique feature of this group is the presence of a seven-membered heterocycle containing an oxygen atom in a diphenyl ether linkage. The known occurrence of these alkaloids is restricted to the genera Dicentra and Corydalis. 

Almost all of the studied plants have been found to contain protoberberines, protopines, and phthalideisoquinolines. The occurrence of aporphines and ben-zophenanthridines is frequent. The secoberbines have been isolated from C. incisa and C. ochotensis. The cularines, which are characteristic of some plants of the genus Corydalis, are also found in the genera Dicentra and Sarcocapnos. 

The cularines are a group of isoquinoline alkaloids with the general structure (1), which incorporates an oxepine system in its molecular skeleton. If the nitrogen is secondary the alkaloid can be called a norcularine. The occurrence of cularine alkaloids in nature seems to be associated mainly with the Fumariaceae family (Sham-ma 1972, Shamma and Moniot 1978). 

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