Syntheses of depsipeptide analogues of the insect neuropeptide proctolin

Four depsipeptide analogues of the insect neuropeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) have been prepared, containing a single ester linkage between Arg1 and Tyr2, Tyr2 and Leu3, and between Pro4 and Thr5, respectively. A didepsipentapeptide containing an ester linkage between Tyr2 and Leu3 and between Pro4 and Thr5, has also been prepared. The depsipeptide 4 is the first example of a backbone-modified proctolin analogue which shows full myotropic activity.