Fmoc-Sar-Sar-Sar-Sar-OH is a protected tetrapeptide consisting of four sarcosine (Sar) residues, a non-chiral derivative of glycine with a methyl group attached to the nitrogen atom. The Fmoc (Fluorenylmethyloxycarbonyl) group protects the N-terminus of the first sarcosine residue, which can be removed under mild basic conditions during peptide synthesis. The C-terminus of the last sarcosine residue is free, indicated by -OH, allowing it to participate in further coupling reactions or modifications. This tetrapeptide can be used to introduce flexibility and alter the conformational properties of peptide chains while maintaining the overall sequence's chemical stability.