Integrated synthesis of 3,4-carbazoquinone alkaloids -Me-carbazoquinocin A, B and D-F.

Carbazole alkaloids carbazoquinocin A-F possessing a 1-alkyl-2-methyl-3,4--carabazoquinone framework were isolated from the microorganism in 1995. Furthermore, they were found to exhibit strong inhibitory activity against lipid peroxidation. Herein, we report the integrated synthesis of -Me-analogues of 5 members of the carbazoquinocin family of natural products, namely, -Me-carbazoquinocin A, B and D-F. We employed an acid-catalyzed, intramolecular benzannulation of indole-appended -enoate propargylic alcohols, which was developed earlier in our laboratory, for the construction of the required carbazole framework. All five natural products were obtained in an overall yield of 50-60%, starting from a commercially available indole.