This paper concerns a synthetic study of the right-hand segment of complestatin, an inhibitor of gp120-CD4 receptor. The effective synthesis of four important precursors for the right-hand segment of complestatin is described. Two of them are the precursor tripeptides for macrolactamization to the right-hand segment of complestatin at the last step and the other two are the precursor tripeptides for ring-closing reaction using Suzuki and Stille coupling, respectively, to the right-hand segment of complestatin at the last step. These compounds and the synthetic procedure will serve for both the synthesis of the right-hand segment and total synthesis of complestatin in the near future. In addition, consideration of the smooth acidic isomerization of complestatin to chloropeptin was carried out by density functional theory (DFT) calculation.