Immuno-Regulating Peptides, I. Synthesis and Structure-Activity Relationships of Thymopentin Analogs

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Abstract
Seventeen peptides related to thymopoietin pentapeptide, L-Arg-L-Lys-L-Asp-L-Val-L-Tyr (thymopentin) were synthesized by the stepwise strategy in solution. Of these, L-Arg-L-Lys-L-Asp and L-Arg-L-Lys-L-Asp-L-Val, shortened from the C-terminus of the pentapeptide, exhibit significant immuno-stimulating potencies, exceeding those of thymopentin, both in vitro [restoration of the azathioprine-inhibited E-rosette formation] and in vivo [hemagglutination assay for IgM in newborn rats] immunological tests. Studies on the structure-activity relationships suggest that the potential active site of thymopoietins is very sensitive to N- and C-terminal elongations of the peptide chain. For thymic hormones, an active site carrying cumulative chemical signals is proposed instead of well-defined active centers.