A small peptide mimic of the Grb2-SH2 domain, which was previously prepared through the template-assisted click approach and exhibited selective A431 tumor growth inhibition both in vitro and in vivo, was further elaborated on to enhance the interaction with target phosphorylated proteins. A conformationally fixed analog was efficiently synthesized by solid-supported ring-closing metathesis and Cu(i)/His-mediated self-activating Huisgen [3+2] cycloadditon as the key steps, and exhibited a 10-fold enhanced affinity to a phosphorylated peptide, a truncated peptide analog of the Grb2-SH2-interacting phosphoproteins. A stronger interaction with the target phosphorylated proteins gave this cyclic analog cytotoxic activity in A431 cells. © 2013 The Royal Society of Chemistry.