Total synthesis of (-)-apratoxin A, 34-epimer, and its oxazoline analogue

Chem Asian J. 2009 Jan 5;4(1):111-25. doi: 10.1002/asia.200800365.

Abstract

A concise and convergent total synthesis of the highly cytotoxic marine natural product apratoxin A is accomplished by an 18-step linear sequence. The high sensitivity of the thiazoline, bearing an adjacent beta-hydroxyl group at the C35-position, results in the assembly process requiring the inclusion of appropriate protecting groups and the careful optimization of all individual transformations. In the synthesis of 3,7-dihydroxy-2,5,8,8-tetramethylnonanoic acid (Dtena), the three reagent-controlled asymmetric reactions enables us to introduce four chiral carbon centers in a dihydroxylated fatty acid moiety. Formation of the hindered ester and sterically-unfavorable N-methylamide bonds were successfully demonstrated. The thiazoline in apratoxin A was constructed by Tf(2)O and Ph(3)PO-mediated dehydrative cyclization, and final macrocyclization was achieved between N-methylisoleucine and proline residues. Moreover, an oxazoline analogue and a C34 epimer of apratoxin A have also been elaborated in a similar approach. This synthetic route would enable assembly of other analogues differing in stereocenters of Dtena and their amino acids.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalysis
  • Cyclization
  • Depsipeptides / chemical synthesis*
  • Depsipeptides / chemistry
  • Oxazoles / chemical synthesis*
  • Oxazoles / chemistry
  • Rhenium / chemistry
  • Stereoisomerism

Substances

  • Depsipeptides
  • Oxazoles
  • apratoxin A
  • Rhenium