The role of (Z)-2,3-didehydrophenylalanine and phenylalanine C-terminal residues in determining the chemotactic activity of formylpeptides

Structure–activity relationship of for-l-Met l-Leu-l-Phe-OMe analogues in human neutrophils

Neutrophils constitute the first line of defence against bacterial invasion. They migrate to infected tissues along a concentration gradient of chemoattractant molecules, the most important of which is for-Met-Leu-Phe-OH (fMLP). Different responses arise from formylpeptides binding to different isoforms of the specific receptor. The aim of the studies reported herein was to clarify (i) the role of fMLP-OMe amide bonds in receptor-ligand cross-linking, (ii) the nature of the group occupying the N- and C-terminal positions, (iii) the features peculiar to the Met, Leu, and Phe receptor pockets, and (iv) the features which determine the specific neutrophil response.

Beta-peptido sulfonamides: for-Met-Leu-Phe-OMe analogues containing taurine and chiral beta-amino-ethanesulfonic acid residues

A series of new beta-peptido sulfonamides, related to the chemotactic tripeptide fMLF-OMe, has been synthesized. The examined 1a,b-7a,b models contain the achiral -HN-(CH(2))(2)-SO(2)- taurine (Tau) residue or the chiral -HN-CH(nBu)-CH(2)-SO(2)- and -HN-CH(iBu)-CH(2)-SO(2)- residues, corresponding to the beta-aminocarboxylic acid counterparts beta(3)-HNle and beta(3)-HLeu, respectively. The biological activity of the new analogues has been determined on human neutrophils and compared with that of the reference ligand as well as that of the previously studied related models. The results are analyzed in terms of structure-activity relationships. The conformational preferences of the new tripeptides 1b and 2b, containing a central chiral beta-amino-ethanesulfonic acid residue, have also been discussed.

Isopeptide bonds in chemotactic tripeptides. Synthesis and activity of lysine-containing fMLF analogs

In order to explore the properties of chemotactic N-formylpeptides containing isopeptide bonds within their backbones, a group of lysine-containing analogs of the prototypical chemotactic tripeptide N-formylmethionyl-leucyl-phenylalanine (fMLF) was synthesized. The new analogs were designed by adding to the HCO-Met or Boc-Met residue a dipeptide fragment made up of Lys and Phe residues joined through Lys N alpha or N epsilon bonds, in all possible combinations. Thus, the following six pairs of tripeptides were synthesized and examined for their bioactivity: RCO-Met-Lys(Z)-Phe-OMe (2a, b), RCO-Met-Lys(Z-Phe)-OMe (3a, b), Z-Lys(RCO-Met)-Phe-OMe (4a, b), Z-Phe-Lys(RCO-Met)-OMe (5a, b), RCO-Met-Phe-Lys(Z)-OMe (6a, b) and Z-Lys(RCO-Met-Phe)-OMe (7a, b), with R=OC(CH3)(3 )and R=H for compounds a and b, respectively. All the new models were characterized fully and their activity (chemotaxis, superoxide anion production and lysozyme release) on human neutrophils determined as agonists (compounds b) and antagonists (compounds a). All N-formyl derivatives 2b-7b are less potent than fMLF-OMe as chemoattractants, but compound 7b exhibits selective activity as superoxide anion producer. Derivatives 2a-7a do not show antagonistic activity towards fMLF induced chemotaxis and O(2)(-) production, however, all these compounds except 4a antagonize lysozyme release by 60%.

Modulation of neutrophil phospholipase C activity and cyclic AMP levels by fMLP-OMe analogues

The N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-OMe (1) analogues for-Thp-Leu-Ain-OMe (2), for-Thp-Leu-Phe-OMe (3), for-Met-Leu-Ain-OMe (4), for-Met-Delta(z)Leu-Phe-OMe (5), for-Met-Lys-Phe-For-Met-Lys-Phe (6), for-Met-Leu-Pheol-COMe (7), and for-Nle-Leu-Phe-OMe (8) have been studied. Some of these have been found selective towards the activation of different biological responses of human neutrophils. In particular, peptides 2 and 3, which evoke only chemotaxis, are ineffective in enhancing inositol phosphate, as well as cyclic AMP (cAMP) levels. On the contrary, analogues 5 and 7, which induce superoxide anion production and degranulation, but not chemotaxis, significantly increase the levels of the two intracellular messengers, as is the case of the full agonists 1 and 6. The Ca(2+) ionophore A23187 also activates phospholipase C (PLC) and increases the nucleotide levels; when tested in combination with peptide 1 or 5, a supra-additive enhancement of cAMP concentration is obtained. The PLC blocker, U-73122, inhibits the formylpeptide-induced inositol phosphate formation, as well as cAMP increase. Moreover, this drug drastically reduces superoxide anion release triggered by 1 or 5, whereas it inhibits to a much lesser extent neutrophil chemotaxis induced by 1 or 2. Our results suggest that: (i) PLC stimulation is involved in cAMP enhancement by formylpeptides; (ii) the activation of PLC by formylpeptides, in conditions of increased Ca(2+) influx, induces a supra-additive enhancement of the nucleotide; (iii) the inability of pure chemoattractants to significantly alter the PLC activity or cAMP level, differently from full agonists or peptides specific in inducing superoxide anion release, appears as a general property. Thus, the activation of neutrophil PLC seems essential for superoxide anion release, but less involved in the chemotactic response.

Bioactive fMLF-OMe analogs containing a N-terminal oximic or formylhydrazonic moiety

In order to obtain chemotactic peptides with selective bioactivity, a new type of structural modification was introduced at the N-terminal position of HCO-Nle-Leu-Phe-OMe. Two groups of analogs have been synthesized both containing a N-terminal residue of the X=C(R)-CO-type replacing the native HCO-NH-CH(R)-CO-. In particular, the A group of pseudopeptides (2a-d) possesses a N-terminal oximic fragment (X=HO-N) and the B group (3a-d) a formylhydrazone fragment (X=HCO-NH-N). These new ligands have been examined for their capacity to induce chemotaxis and other cellular responses such as superoxide anion production and lysozyme release; although significantly active as chemoattractants they have been found to be practically devoid of secretagog activity, thus exhibiting selective behavior. The adopted chemical modification seems extensible in designing a new class of pseudopeptides (hydrazonopeptides) structurally related to both hydrazinopeptides and peptides containing alpha,beta-unsaturated residues.

Chemotactic peptide analogues. Centrally constrained chemotactic N-formyltripeptides: synthesis, conformation, and activity of two new analogues

The role exercised by the central residue of the chemotactic N-formyltripeptide HCO-Met-Leu-Phe-OMe (fMLP-OMe) in controlling both the backbone conformation and the biochemical activity is the subject of recent interest. Here, two new centrally constrained fMLP-OMe analogues, namely HCO-Met-azaPro-Phe-OMe (4) and HCO-Met-(gamma-lactam)-Phe-OMe (6) have been synthesized and their CDCI3 solution conformation and activity have been studied. The azapeptide 4 adopts beta-folded conformation with the azaPro residue at the i+2 position and an intramolecular H-bond involving the formylic oxygen and the Phe NH. The gamma-lactam tripeptide 6 prefers a semi-extended backbone conformation. When tested on human neutrophils both the new models were found practically devoid of biological activity. The role exerted by the NH groups as well as by the conformational preferences is discussed.