5-7-6 daphnane skeleton

The 5-7-6-tricyclic framework exists in many natural products, which often shows biological activities. For example, phorbol 40 (Figure 5.1) is extensively used in studies of tumor promotion because of its ability to activate protein kinase The related 5-7-6 daphnane skeleton is exemplified by the antileukemic agent gnidilatin (41) and by the irritant resiniferatoxin, which also possesses analgesic properties. However, the stereocontrolled construction of such 5-7-6-tricyclic systems is still a challenge. ... 

Daphnezomine L (48) was close structurally to a biogenetic intermediate between the secodaphnane and daphnane skeletons. 

A possibly biomimetic transformation of the secodaphnane to the daphnane skeleton with various Lewis acids has been investigated (Scheme 18,26) [73],... 

Two new daphnezomine L-type alkaloids, daphnezomine L methyl ester (38), [26] and calycinumine B (39) [29], were reported (Figure 9). Daphnezomine L methyl ester (38) is structurally close to a hypothetical biogenetic intermediate between the secodaphnane and daphnane skeletons. Calycinumine B (39) features an imprecedented heteroatom-containing adamantane -like western hemisphere of daphnezomine L-type alkaloid. 

C. H. Heathcock, D. Joe, Daphniphyllum Alkaloids. 17. A possibly biomimetie transformation of the secodaphnane to the Daphnane Skeleton, Journal of Organic Chemistry 60 (1995) 1131-1142. 

Aza Analogues of the Tricyclic Skeleton of Daphnane and the ABC Ring System of Phorbol... 

Scheme 16.38 Approach to the tricyclic daphnane/tigliane skeleton via n.21-shift.

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