Oxidation of the indolo[2,3-a]carbazole 15, readily obtained in six steps from indigo, followed by deprotection results in formation of the indolo[3,2-j]phenanthridine quinone alkaloid calothrixin B 2, demonstrating the viability of the proposed biosynthetic route to this unique ring system. (c) 2006 Elsevier Ltd. All rights reserved.
Oxidation of the indolo[2,3-a]carbazole 15, readily obtained in six steps from indigo, followed by deprotection results in formation of the indolo[3,2-j]phenanthridine quinone alkaloid calothrixin B 2, demonstrating the viability of the proposed biosynthetic route to this unique ring system. (c) 2006 Elsevier Ltd. All rights reserved.