Synthesis and biological activity of N-methylated analogues of neurokinin A

Limited conformational constraints have been introduced in the sequence of the C-terminal heptapeptide NKA(4-10) by N-methylation of individual peptide bonds and the biological activities of the peptides thus obtained were evaluated on three in vitro preparations sensitive and quite selective for each of the naturally-occurring neurokinins, in order to assess the effect of N-methylation on receptor selectivity. The analogue methylated in position 7, namely [MeVal7] NKA(4-10) shows some selectivity for the NK-P receptor, while none of the tested compounds appear to be selective for the NK-A receptor.