Total Synthesis of Suberitines A-D Featuring Tunable Biomimetic Late-Stage Oxidative Dearomatization and Acetalization.

Abstract

Aaptaminoids are a unique family of marine alkaloids bearing a benzo[de][1,6]-naphthyridine core. This work describes the first total synthesis of suberitines A-D (1-4), four typical dimeric natural aaptaminoids, employing a step-saving bidirectional strategy. Key methods applied in the total synthesis include a cationic cascade to construct the bis-isoquinoline(s) with Hendrickson reagent-mediated Friedel-Crafts-type cyclization and eliminative aromatization, and a Bronsted acid-promoted Vilsmeier cyclization to generate the naphthyridine(s). The conditionally tunable PIDA-mediated oxidative dearomatization and subsequent methanolysis or hydrolysis successfully served as a powerful biomimetic tool to elaborate the essential oxygenated functionalities of suberitines A-D (1-4) in proper solvent-combinations at the final stage of total synthesis. The biomimetic proposal employed in the late-stage redox interchanges of related natural products was eventually supported by the isolation of synthetic intermediate 23 a as a natural product from the same natural source. Biological screening revealed that five of the synthetic samples including two natural suberitines and three full-skeleton natural product-like intermediates exhibited low micromolar inhibitory activities against the growth of cancer cell line K562.