For-Met-Lys-Phe-For-Met-Lys-Phe-: a new cyclic analogue of the chemotactic formylpeptides.

As a continuation of the studies on chemotactic N-formylpeptides, we report here the synthesis and activity of a new cyclic analogue of the prototypical ligand For-Met-Leu-Phe-OMe. The new compound For-Met-Lys-Phe-For-Met-Lys-Phe- (4) contains a 20-membered cyclic moiety made up of a dimeric -Lys-Phe- sequence in which For-Met is attached to each Lys alpha-NH2 and hence remains outside the ring. The conformation in the crystal of the cyclic precursor of 4, namely Boc-Lys-Phe-Boc-Lys-Phe- (2) and the activity of the structurally related linear analogue For-Met-Lys(Z)-Phe-OBzl (6), have also been examined. The new analogues 4 and 6 are active as chemoattractants, secretagogues, and superoxide anion generating agents, when tested on human neutrophils. The structure-activity relationship is discussed and related to that of a previously studied cyclic model.