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A New Total Synthesis of an Indolo[3,2-j]phenanthridine Alkaloid Calothrixin B. -The synthesis involves an allene-mediated electrocyclic reaction (II)→(III) as the key step. -(TOHYAMA, S.; CHOSHI, T.; MATSUMOTO, K.; YAMABUKI, A.; IKEGATA, K.; NOBUHIRO, J.; HIBINO*, S.; Tetrahedron Lett. 46 (2005) 32, 5263-5264; Fac. Pharm. Pharm. Sci., Grad. Sch. Pharm. Pharm. Sci., Fukuyama Univ., Fukuyama, Hiroshima 729-02, Japan; Eng.) -Roy 46-193

Total Synthesis of Bioactive Indolo[3,2-j]phenanthridine Alkaloid, Calothrixin B.-The synthesis of calothrixin B (V) is investigated by using three routes. The common strategy is based on an allene-mediated electrocyclic reaction of a 6π-electron system involving one or two indole bonds for construction of an appropriate 4-oxygenated 2,3,4-trisubstituted carbazole (III) or a 6-oxygenated 5-methylindolocarbazole (VIII). Oxidation of the methyl group of (III) and subsequent reduction of the nitro group of (IV) yield the pentacyclic calothrixin framework, which is oxidized to provide the title compound (V). In a biomimetic pathway, the fully protected formylindolocarbazole (IX) affords title compound (V) via N-methoxymethyl-calothrixin B (X). -(TOHYAMA, S.; CHOSHI*, T.; MATSUMOTO, K.; YAMABUKI, A.; HIEDA, Y.; NOBUHIRO, J.; HIBINO, S.; Heterocycles 82 (2010) 1, 397-416, http://dx.doi.org/10.3987/com-10-s(e)11 ; Fac. Pharm. Pharm. Sci., Grad. Sch. Pharm.