SYNTHESIS AND BIOLOGICAL-ACTIVITY OF LOCUST AKH-I AND ITS ANALOGS WITH MODIFICATIONS AT THE THREONINE RESIDUES

A convenient method of synthesis, using a combination of solid and liq uid phase methodology, for locust Adipokinetic Hormone-I (AKH-I) and i ts analogues with modifications at the threonine residues are reported . The N-terminal nonapeptide acid of AKH-I is synthesized in the solid phase using the 2-chlorotrityl chloride resin and the Fmoc/t-Bu strat egy. Quantitative cleavage of the nonapeptide acid from the resin, wit h the tert-butyl type side-chain protection intact, is achieved with a mixture of acetic acid/trifluoroethanol/dichloromethane. The nonapept ide acid is then coupled in solution to the threonine derivatives, H-T hr-NH2 or H-Thr(Bzl)-NH2, with the DCC/HOBt method. The efficiency of this approach in the synthesis of AKH-I is demonstrated by the high yi elds and purity of the synthesized peptides. All the synthesized pepti des were tested in two ways: first, in a lipid mobilization assay in l ocusts in vivo; and second, in a novel assay in vitro concerned with t he uptake of radiolabelled acetate into locust tissue. Replacement of the hydroxyl hydrogen in Thr(5) of locust AKH-I by the bulky and highl y lipophilic tert-butyl group reduced the potency markedly, whereas ef ficacy is unaffected, but when the hydroxyl hydrogen of Thr(10) in AKH -I is replaced by a benzyl group, the activity of the resulting analog ue is identical to that of the natural peptide. Structure-activity rel ationships are discussed. (C) Munksgaard 1994.