[Synthesis and biological properties of a cyclic analog of ACTH-(5-14)-decapeptide].

A cyclic analogue and the corresponding linear segment of the corticotropin molecule, namely ACTH-(5-14)- and [cyclo (Glu gamma-epsilon Lys)]ACTH-(5-14)-decapeptide, both including the specific and unspecific active centers of the ACTH molecule, have been synthesized and studied. The cyclic structure is fixed by amide bond between the glutamic acid and lysine side chains. Condensation of fragments has been realized by azide or DCC/HOBT methods. Cyclization has been achieved using diphenylphosphorylazide. The cyclic analogue has full steroidogenic activity, while its melanotropic activity is 3 orders of magnitude higher than that of the linear decapeptide.