Macrocyclization studies and total synthesis of cyclomarin C, an anti-inflammatory marine cyclopeptide

The studies on macrocyclization at possible sites toward the total synthesis of cyclomarin C are described. The results showed that both Trp and Phe derivatives involved in the target could not be the terminals of the final linear peptide precursors. Additionally, preparation of corresponding dipeptides with an N-methyl amide bond is not favorable in the synthesis of linear precursors. Site d was finally proved a proper site for the cyclopeptide formation, and the corresponding head-to-tail macrocyclization was achieved under mild conditions and gave repeatable and satisfactory yields.