Synthesis of an actinomycin-related peptide lactone from the corresponding cyclic pentapeptide by N,O-acyl shift

The N,O-acyl shift was investigated as a method for the synthesis of an O-peptide or peptide lactone from a linear or cyclic peptide respectively. Protected derivatives of glycyl-L-threonine could be converted to O-peptides by the action of HCl/dioxane at room temperature and N-acylated under conditions which precluded a reverse O,N-acyl shift. For effecting N,O-acyl shift in cyclo(Thr-D-Val-Pro-Sar-MeAla) this reagent was unsatisfactory and p-toluenesulfonic acid in dioxane at 80 degrees was used instead. The resulting crystalline peptide lactone p-toluenesulfonate salt was N-acylated with 3-benzyloxy-4-methyl-2-nitrobenzoyl chloride to afford a known intermediate in the synthesis of 5,5'-MeAla actinomycin D. This approach constitutes a novel synthetic route to actinomycins and potentially to other peptide lactone antibiotics.