Synthesis and biological evaluation of QRSTUVWXYZA′ domains of maitotoxin

The synthesis of QRSTUVWXYZA′ domains 7, 8, and 9 of the highly potent marine neurotoxin maitotoxin (1), the largest secondary metabolite isolated to date, is described. The devised synthetic strategy entailed a cascade Takai-Utimoto ester olefination/ring closing metathesis to construct ring Y, a hydroxydithioketal cyclization/methylation sequence to cast ring X, a Horner-Wadsworth-Emmons coupling of WXYZA′ ketophosphonate 11 with QRSTU aldehyde 12 to form enone 10, and a reductive hydroxyketone ring closure to forge ring V. 2D NMR spectroscopic analysis and comparison of ¹³C chemical shifts with those of the corresponding carbons of maitotoxin revealed close similarities supporting the originally assigned structure of this region of the natural product. Biological evaluations of various synthesized domains of maitotoxin in this and previous studies from these laboratories led to fragment structure-activity relationships regarding their ability to inhibit maitotoxin-elicited Ca²⁺ influx in rat C6 glioma cells.