Paraisariamides: Cycloheptapeptide Toxins from Entomopathogenic Fungi ( <i>Paraisaria</i> spp.) That Inhibit Total Protein Synthesis

Insect-associated fungi are prolific producers of peptidic natural products with potent biological activities. <i>Paraisaria</i> is a genus of insect-pathogenic fungi (Family Ophiocordycipitaceae) in the Order Hypocreales, which also includes other <i>Cordyceps</i>-like fungi. Such fungi are increasingly used as functional foods and nutraceuticals, but <i>Paraisaria</i> may also be unintentionally consumed through infected, potentially toxic, edible insects. Here we report the discovery, isolation, and structure elucidation of paraisariamides A-D (<b>1</b>-<b>4</b>) from <i>Paraisaria cascadensis</i> and paraisariamides E-H (<b>5</b>-<b>8</b>) from <i>P. insignis</i>. Total synthesis of <b>1</b> and <b>5</b>-<b>8</b> was instrumental for comprehensive structure assignment and provided pure compounds for advanced biological testing. The paraisariamide family of <i>N</i>-methylated cyclic heptapeptides has been detected in all <i>Paraisaria</i> specimens analyzed to date from a variety of ecological niches. Paraisariamides A-H (<b>1</b>-<b>8</b>) display differential cell-type specific toxicity to human cancer cells, and we demonstrate that the most cytotoxic paraisariamides E-H (<b>5-8</b>) potently and rapidly inhibit mammalian protein synthesis. Molecular cartography was used to visualize the spatial distribution of paraisariamides in a lyophilized specimen of a beetle larva parasitized by <i>P. insignis</i>. Localization of paraisariamides to the fungal endosclerotium within the host larva is consistent with a role in localized disruption of host protein synthesis.