Total Synthesis of Mycenarubin A, Sanguinolentaquinone and Mycenaflavin B and their Cytotoxic Activities

Here we report the first total synthesis of the fungal alkaloids mycenarubin A, sanguinolentaquinone and mycenaflavin B. The pyrroloquinoline alkaloid mycenarubin A was obtained in 10 steps (21% total yield, 92% ee) from the known key precursor 6,7-bis(benzyloxy)indole by an asymmetric alkylation and a biomimetic ring closure as the key steps. The indolo-6,7-quinone sanguinolentaquinone was obtained in eight steps (28% total yield). Mycenaflavin B was also obtained in eight steps starting from the same key precursor (total yield 15%) by a biomimetic ring closure and an acid-catalysed decarboxylation reaction as the key steps. The cytotoxic activities of mycenarubin A and mycenaflavin B were evaluated against mouse fibroblasts (L929) and human malignant melanoma cells (RPMI-7951).