Calothrixin synthesis

Bennasar et al. reported a new radical-based route for the synthesis of calothrixin B (378) (869). This synthesis starts from the 2,3-disubstituted N-Boc indole 1558 and uses a regioselective intramolecular acylation of a quinoline ring as the key step for the construction of the calothrixin pentacyclic framework. Chemoselective reaction of in s/fM-generated 3-lithio-2-bromoquinoline [from 2-bromoquinoline 1559 with LDA] with the 3-formylindole 1558 followed by triethylsilane reduction of the... 

Recently, Moody et al. reported a biomimetic synthesis of calothrixin B (378) by oxidation of Hibino s 6-formylindole[2,3-fl]carbazole 1555 (870). The key intermediate 6-formyl-indole[2,3-fl]carbazole was readily obtained in six steps from indigo (1458). Using Somei s procedure, indigo (1458) was transformed to the cis-chlorohydrin 1461 in three steps and 50% overall yield (see Scheme 5.247). The reduction of the chlorohydiin 1461 gave 5-hydroxy-indolo[2,3-fl]carbazole 1564, and subsequent Vilsmeier formylation delivered the desired 6-formyl-indole[2,3-fl]carba-zole 1565 in 45% yield. Reaction of hydroxy-indolocarbazole 1565 with an excess of chloromethyl methyl ether (MOMCI) afforded the tiis-MOM-protected compound 1555. Following Hibino s approach, the tris-MOM-protected indolocarbazole 1555... 

Choshi, T, and Hibino, S. (2009) Progress towards the total synthesis of the bioactive calothrixins A and B. Heterocycles, T7, 85-97. 

---