Total Synthesis of Bistratamide D.
The total synthesis of the macrocyclic hexapeptide bistratamide D is reported. The synthetic strategy involved assembly of enantiomerically pure oxazole, thiazole, and oxazoline segments derived from amino acids. Macrocyclization of the hexapeptidic aminooxazoline-oxazole-thiazole carboxylic acid fragment was accomplished by activation with O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU).