Isolation, enantioselective total synthesis and structure determination of the anthrapyran metabolite SS 43405-e

The first enantioselective total synthesis of the anthrapyran metabolite SS 43405-e, isolated from a marine-derived streptomycete, is described, which also allows the determination of the so far unknown absolute (R) configuration of the natural product. For the synthesis the bromoanthracene derivative 3 is lithiated and coupled with the enantiopure aldehyde (S)-4 to give 9, which is oxidatively transformed into the corresponding anthraquinone 10 and further into the ketone 2. The final step is the cyclization of 2 under acidic conditions to give the desired antibiotic (S)-1. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)