A highly stereocontrolled synthesis of the JKLM ring fragment of ciguatoxin has been achieved. The present synthesis starts with methyl 4,6-O- benzylidene-2-deoxy-2-C-methyl-α-D-altropyranoside, whose configurations and substituents at C2-C5 correspond to those at C46-C49 of ciguatoxin, and involves as the key step base-induced 7-endo selective cyclization of a hydroxy epoxide for the efficient construction of the fully substituted oxepane ring K. Construction of the spiroether ring M was achieved by introduction of an allyl group to the ring L lactone followed by asymmetric dihydroxylation to install the C54 stereogenic center and acid-induced spiroketalization to furnish the protected KLM ring system. Finally, ring J was constructed by the method of Nicolaou to complete the synthesis of the JKLM ring fragment. The synthesis of a carboxylic acid derivative and its conjugation to carrier proteins to give an artificial antigen for development of an immunoassay system for the parent toxin molecule are also reported.
ASJC Scopus subject areas
- Organic Chemistry