Total synthesis of (-)-ulapualide A, a novel tris-oxazole macrolide from marine nudibranchs, based on some biosynthesis speculation.

A new, second generation, total synthesis of ulapualide A (1), whose stereochemistry was recently determined from X-ray analysis of its complex with the protein actin, is described. The synthesis is designed and based on some speculation of the biosynthetic origin of the contiguous tris-oxazole unit in ulapualide A, alongside that of the related co-metabolites that contain only two oxazole rings, e.g.

CuCl-mediated intramolecular oxidative coupling of aryl- and alkenyltrimethylstannane functions.

[reaction: see text] The syntheses of bis-trimethylstannanes 8, 10, 12-14, 16, 18, 21, and 22 are described. Treatment of these substances with approximately 5 equiv of CuCl in DMF at rt for 30-60 min effects, in each case, oxidative coupling between the two sp2 carbon centers bearing the Me3Sn function to produce good-to-excellent yields of tricyclic products 23-31, respectively.