Pyrrolo- carbazole core

Dictyodendrins A—E are a family of marine natural products, isolated by Fuse-tani and Matsunaga from the sponge Dictyodendrilla verongiformis (2003 JOC2765). Dictyodendrins have a unique pyrrolo[2,3-c]carbazole core. They exhibit strong telomerase inhibitory activity and their function exerts an important effect on relevant vital processes such as aging and cancer. 

The synthesis of dictyodendrins A and F was realized through a sequential C—H functionahzation strategy inclusive of an initial C3 arylation, a site-selective double C—H alkylation with an aryldiazoacetate derivative and a subsequent Suzuki-Miyaura cross-coupHng with indole-3-boronic acid pinacol ester 107 (2015JAC644). A formal 67r-electrocyc-lization of the resultant tetrasubstituted pyrrole 108 fashioned the required pyrrolo-[2,3-c]carbazole core (109) which was further elaborated to the targets. 

Hirao, S., Sugiyama, Y, Iwao, M., and Ishibashi, F. (2009) Synthetic approach to telomerase inhibitor dictyodendrin B Synthesis of the pyrrolo[2,3-c]carbazole core. Biosti. Biotechnol. Biochem., 73,1764-1772. 

Hill described the Pd(OAc)2-oxidative cyclization of bisindolylmaleimides (e.g., 49) to indolo[2,3-a]pyrrolo[3,4-c]carbazoles (e.g., 50) [69], which is the core ring system in numerous natural products, many of which have potent protein kinase activity [70]. Other workers employed this Pd-induced reaction to prepare additional examples of this ring system [71, 72]. Ohkubo found that PdClj/DMF was necessary to prevent acid-induced decomposition of benzene-ring substituted benzyloxy analogues of 49, and the yields of cyclized products under these conditions are 85-100% [71]. 

Structurally, most members of this family are characterized by a core consisting of an indolo[2,3-a]carbazole, which is frequently fused to a pyrrolo[3,4-c] unit. The chromophore is often decorated with a carbohydrate that is attached either through a single N-glycosidic bond, as in rebeccamycin 1 (REB), or through two C-N bonds, as in staurosporine 2 (STA). Another key structural difference between REB and STA resides at the pyrrole moiety, consisting of an imide function in the former but an... 

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