Synthesis, conformation, and activity of HCO-Met-^Z Leu-Phe-Ome, an active analogue of chemotactic N-formyltripeptides

G. Pagani Zecchini ¹, M. Paglialunga Paradisi ¹, I. Torrini ¹, G. Lucente ^{1 *}, E. Gavuzzo ², F. Mazza ², G. Pochetti ², M. Paci ³, M. Sette ³, A. Di Nola ⁴, G. Veglia ⁴, S. Traniello ⁵, S. Spisani ⁵

¹Dipartimento di Studi Farmaceutici and Centro di Studio per la Chimica del Farmaco del CNR, Università La Sapienza, 00185 Roma, Italy
²Istituto di Strutturistica Chimica G. Giacomello CNR, C.P. n. 10, 00016 Monterotondo Stazione, Roma, Italy
³Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma, V. O. Raimondo, 001 73 Roma, Italy
⁴Dipartimento di Chimica, Università La Sapienza, 00185 Roma, Italy
⁵Istituto di Chimica Biologica, Università di Ferrara, 44100 Ferrara, Italy

Abstract

In order to induce a -turn conformation into the chemotactic linear tripeptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), the new analogue N-formyl-L-methionyl-^Zleucyl-L-phenylalanine methyl ester [ ^ZLeu]²f MLP-OMe (1) has been synthesized. The conformational and biochemical consequences of this chemical modification have been determined. Analogue 1 has been synthesized by using N-carboxy-(Z)-,-didehydroleucine anhydride as key compound to introduce the unsaturated residue at the central position of the tripeptide 1. The x-ray analysis shows that 1 adopts in the crystal a type II -turn conformation in which the new residue occupies the (i + 2) position, and an intramolecular H bond is formed between the formylic oxygen and the Phe NH. ¹H-nmr analysis based on nuclear Overhauser effect measurements suggests that the same folded conformation is preferred in CDCl₃ solution; this finding is also supported by molecular dynamics simulation. The biological activity of 1 has been determined on human neutrophils (polymorphonuclear leukocytes) and compared to that shown by f MLP-OMe. Chemotactic activity, granule enzyme release, and superoxide anion production have been determined. Analogue 1 is practically inactive as chemoattractant, highly active in the superoxide generation, and similar to the parent in the lysozyme release. The conformational restriction imposed on the backbone by the presence of the unsaturated residue is discussed in relation with the observed bioselectivity. © 1993 John Wiley & Sons, Inc.