Syntheses of Cytosporones A, C, J, K, and N, Metabolites from Medicinal Fungi

The syntheses of the fungal metabolites cytosporones A, (+/-)-C, and N are reported. And the syntheses of cytosporones J and K are described for the first time. The preparation of racemic cytosporone J and racemic cytosporone K, natural products containing the rare 3-isochromanone substructure, was achieved in 8 linear steps with an overall yield of 45% and 7 linear steps in 46% yield, respectively, resulting in the complete characterization of these compounds for the first time. The key steps included a recently described homologation of benzoic acid to the analogous phenyl acetate using Birch reductive alkylation conditions, acylation of the appropriate phenyl acetate derivative, and a selective reduction and spontaneous biomimetic lactonization to yield the 3-isochromanone skeleton. The synthesized natural products were evaluated for their biological activity against several clinical strains of human pathogens with all compounds displaying weak antimicrobial activity.