Structure–activity relationships of cyclic and linear peptide T analogues

Using the potent cyclic peptide T analog-Thr-Thr-Asn-Tyr-Thr-Asp- as parent compound, a series of analogues were synthesized and their potencies in a monocyte chemotaxis assay were compared with those of correspondingly modified linear peptides. Structure-activity relationships observed with cyclic compounds did not always parallel those determined with linear analogues. -Thr-Hse-Asn-Tyr-Thr-Asp- showed the highest affinity to CD4 receptor of monocytes of any peptide thus far studied. It also proved to be highly resistant to degradation by plasma or brain enzymes.