Synthesis and Biological Activity of Peptides Related to Eledoisin. II. Hexapeptide Amides Containing N-Methylamino Acids

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Abstract
Eledoisin-like hexapeptides were synthesized in order to obtain longer-lasting hypotensive analogs. A part of the amino acid of the standard pep tide, H–Lys–Phe–Ile–Gly–Leu–Met–NH2 (1), was replaced by N-methylamino acid. It was found, in these syntheses, that when the C-terminal amino acid of a carboxy component was an N-methylamino acid, a system of dicyclohexylcarbodiimide plus 1-hydroxybenzotriazole was a useful coupling agent. With regard to the hypotensive effect in rabbits, H–Lys–Phe–Melle–Gly–Leu–Met–NH2 (2) and H–Lys–Phe–Ile–Gly–Melle–Met–NH2 (6) show much less activity; H–Lys–MePhe–Ile–Gly–Leu–Met–NH2 (3) and H–Lys–MePhe–Ile–Gly–MeLeu–Met–NH2 (7) show a substantial activity, though weaker than the standard one. On the other hand, H–Lys–Phe–Ile–Gly–MeLeu–Met–NH2 (5) and H–Lys–Phe–Ile–Sar–Leu–Met–NH2(4) show a higher activity than 1. These results indicate that, in some cases, the replacement of an amide bond by an N-methylamide bond without any change in the side chain of amino acid would have an important influence on the activity. The duration of the action of N-methypeptildes synthesized was unexpectedly of the same order of magnitude as that of 1.