Structure-activity studies of the C-terminal segment of structurally reduced analogues of ET-1

Structurally reduced analogues of endothelin-1 (ET-1) were synthesized by linking via aminocaproic acid (Aca) the segment 3-11 of ET-1 to C-terminal fragments of various lengths [16-21, 17-21,...,21]. Analogues were studied in their linear or cyclic form in the absence or presence of a formyl group on the Trp21 side-chain, and their biologic activities were tested using guinea pig lung parenchymal strips. The absence of the first disulfide bridge and the presence of the Aca spacer caused a slight decrease in activity. The presence of His16 is essential for the contractile activity of the monocyclic peptides. Formylation of these monocyclic analogues did not modify this behavior. Similarly, linear analogues carrying S-acetamidomethyl (Acm) functions and an Aca linker were still active. However, most formylated linear derivatives were partial agonists, whereas the addition of His16 caused a decrease in contractile activity. In these latter analogues, molecular modeling studies suggested that formylation produces different conformations.