Total Synthesis of Antiausterity Agent Callistrilone O Reveals Promising Antitumor Activity in a Melanoma Homograft Mouse Model

Abstract The antiausterity strategy in anticancer drug discovery has attracted much attention as a way to exterminate cancer cells under nutrient deprived conditions which are commonly found in solid tumors. These tumors under low nutrient stress are known to be malignant and often resist conventional drug therapy. As a potential drug candidate, we focused on the meroterpenoid natural product callistrilone O which has demonstrated extremely potent antiausterity properties toward PANC‐1 pancreatic carcinoma in vitro . Here, we report for the first time the total synthesis of callistrilone O in seven steps from phloroglucinol. A Friedel‐Crafts‐type Michael addition and an oxidative [3+2] cycloaddition with Fetizon's reagent were used to construct the molecular skeleton. The preferential cytotoxicity of callistrilone O was also evaluated with multiple starvation‐resistant cancer cell lines under low nutrient conditions. Furthermore, callistrilone O was found to strongly suppress B16 melanoma tumor growth without critical toxicity in vivo . Overall, this study presents a novel anticancer agent candidate from natural products with a concise synthetic route which can be readily applied to the synthesis of derivatives.