Syntheses of thyrotropin-releasing hormones (TRH) (Schaf) and related peptides

The syntheses of seven tripeptide isomers containing L -histidine, L -proline and L -glutamic acid residues, the same as found in the natural thyrotropin-releasing hormone (TRH), are reported. In addition L -pyroglutamyl-L -histidyl-L -proline and its amide as well as N^α-acetyl-L -glutamyl-L -histidyl-L -proline are described. Whereas eight peptides are inactive and L -pyroglutamyl-L -histidyl-L -proline shows a slight TRH activity, L -pyroglutamyl-L -histidyl-L -proline-amide has the full biological activity of the isolated thyrotropin-releasing hormone and, at the present state of knowledge, seems to be identical with it.