Synthesis of the tripeptide L-Trp-L-Ser-L-Glu. Comparison of its biological activity with that of the delta-sleep-inducing-peptide (DSIP).

In order to test the specificity of the natural Delta-Sleep-Inducing-Peptide (DSIP), a tripeptide with the same N-terminal amino acid was synthesized. The synthesis of the new tripeptide L-Trp-L-Ser-L-Glu was carried out by the method of the mixed anhydride. Protecting groups were all oxygen-bound benzyl groups. The physical-chemical data of the newly synthesized peptides are reported. The biological activity of the tripeptide was assayed by intraventricular infusion in the rabbit under the same conditions as for the DSIP. The effects of the tripeptide on the EEG could not duplicate those of DSIP which induced a marked increase of delta activity, typical for orthodox 'Slow Wave Sleep' (SWS).