Syntheses of analogues of the insect neuropeptide proctolin containing an oxazole ring as an amide bond replacement.

[structure: see text]. Three oxazole analogues of the insect neuropeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) have been prepared, containing a single oxazole between Tyr and Pro and between Pro and Thr, respectively. A compound containing an oxazole moiety between Tyr and Pro and between Pro and Thr has also been prepared. All compounds have been tested for myotropic activity.