Development of Grb2-SH2 domain antagonists is considered to be an effective and non-cytotoxic strategy to develop new antipro-liferative agents because of their potential to shut down the Ras signaling pathway. We developed a concise route for the efficient synthesis of G1TE analogs on solid phase. Using this route, a series of cyclic peptides that do not rely on phosphotyrosine or its mimics were designed and synthesized based upon the phage library-derived cyclopeptide, ME Considering that Gly(7) plays prominent roles for G1TE binding to the Grb2-SH2 domain, we introduced different amino acids in the 7th position. The D-Ala(7)-containing peptide 3 demonstrates improved binding affinity by adopting favorable conformation for protein binding. This can be rationalized by molecular modeling. The optimization at the Leu(2) position was also studied, and the resulting cyclopeptides exhibited remarkably improved binding affinity. Based upon these global modifications, a highly potent peptide ligand 9 was discovered with a K-d = 17 nM, evaluated by Biacore binding assay. This new analog is one of the most potent non-phosphorus-containing Grb2-SH2 antagonists reported to date. This potent peptidomimetic provides a new template for the development of non-pTyr containing Grb2-SH2 domain antagonists and acts as a chemotherapeutic lead for the treatment of erbB2-related cancer. Published by Elsevier Inc.