Synthesis and applications of cyclopeptides and depsipeptides

A solid phase protocol has been devised for the synthesis of linearprecursors to cyclic depsipeptide analogues of dolastatin D.t-Butyldimethylsilyl groups were used for hydroxy group protection, withdeprotection being carried out by t-butyl ammonium fluoride. HATU and PyBropwere successful in coupling highly hindered residues and in depside bondformation. Cyclic peptide analogues, cycloArg-Gly-Asp-d-Phe-Lys(or Tyr)]have been synthesised and modified for use as carrier molecules for thetransport of radio isotopes (¹¹¹In and ¹²⁵I)into blood platelets as prototypes for medical imaging.