Synthesis of proctolin analogues and their cardioexcitatory effect on cockroach, Periplaneta americana L., and yellow mealworm, Tenebrio molitor L.

Five proctolin analogues modified in position 2 of the peptide chain by (4‐NH2)‐ (I), (4‐NO2)‐ (II), (4‐NMe2)‐ (III), (4‐OMe)‐L‐phenylalanine (IV) and β‐(cyclohexyl‐4‐OMe)‐L‐alanine (V) were synthesized by conventional liquid phase method. Biological activity of the obtained peptides was investigated in cardioexcitatory test on two insect species, cockroach, Periplaneta americana L., and yellow mealworm, Tenebrio molitor L. Peptides I–IV exhibited higher activity than proctolin itself.