Synthesis and activity of new linear and cyclic peptide T derivatives.

Linear and head to tail cyclic hexapeptide analogs (Xaa-Thr-Thr-Asn-Tyr-Thr, Xaa = D-Asp or D-iso-Asp) of peptide T were prepared and tested for human monocyte chemotaxis. All new compounds showed significant bioactivity. In particular, the conformational restriction introduced into cyclo(-D-iso-Asp-Thr-Thr-Asn-Tyr-Thr-) was very suitable for CD4 receptor binding. The cyclic peptides also proved to be highly resistant to degradation by plasma or brain enzymes.