Synthesis of dicarba-cyclooctapeptide Somatostatin analogs by conventional and MW-assisted RCM: A study about the impact of the configuration at Cα of selected amino acids

•Cyclooctapeptides dicarba-analogues of Somatostatin containing d or l-allylglycine.•MW-driven on-resin Ring Closing Metathesis (RCM) of linear octapeptides.•The stereochemistry of strategic amino acids influences the cyclization yield.•Good to high yields and short reaction times achieved by microwave-assisted RCM.•Variable ratio of E/Z stereoisomers due to the sequence and cyclization method.