Giampiero Pagani Zecchini

Effect of cyclic AMP level reduction on human neutrophil responses to formylated peptides

The increase in human neutrophil cyclic adenosine monophosphate (cAMP) levels evoked by formylated peptides is significantly reduced in the presence of MDL 12330A, SQ 22536, GDPssS and clonidine, which inhibit the adenylyl cyclase system by acting at different sites in this enzyme complex. A similar effect is exerted by adenosine deaminase and dipyridamole, which alter the extracellular adenosine concentration. Neutrophil preincubation with adenylyl cyclase inhibitors or dipyridamole reduces chemotaxis and superoxide anion production triggered by peptides; adenosine deaminase, on the contrary, has no effect on neutrophil responses. Our results seem to indicate that: (1) the peptide-induced increase in neutrophil cAMP is due mainly to an action on the adenylyl cyclase system; (2) an enhancement of this cyclic nucleotide, even slight and necessarily transient, is required for chemotaxis and O2 production induced in neutrophils by formylated peptides; and (3) cAMP does not represent the crucial second messenger for adenosine in the modulation of neutrophil responses.

γ-Turn conformation induced by α,α-disubstituted amino acids with a cyclic six-membered side chain

Abstract 4-Aminotetrahydrothiopyran-4-carboxylic acid (Thp) is an unusual achiral cyclic α,α-disubstituted amino acid mimicking the natural Met residue. The conformational energy map computed for Ac-Thp-NHMe shows that the γ-turn is the lowest minimum. 1 H-NMR and IR studies performed on For-Thp-Leu-OMe ( 2a ), a short peptide unable to give a 4…>1 H-bond, indicate that the γ-turn is adopted in CDCl 3 solution, whereas is not retained in (CD 3 ) 2 SO. An analogous conformational behaviour in solution has been observed for the strictly related For-Ac 6 c-Leu-OMe ( 2b ), containing 1-aminocyclohexane carboxylic acid (Ac 6 c).

Formylpeptides trigger selective molecular pathways that are required in the physiological functions of human neutrophils

For-Met-Delta(z)Leu-Phe-OMe ([Delta(z)Leu(2)]) is a conformationally restricted for-Met-Leu-Phe-OMe (fMLP-OMe) analogue able to discriminate between different responses of human neutrophils. In contrast, [Delta(z)Leu(2)] significantly activates the transduction pathways-involving Ca(2+), inositol phosphate, and cyclic AMP (cAMP) enhancement, as is the case with the full agonist fMLP-OMe. Here, we have studied the specific involvement of protein kinase C (PKC) isoforms and mitogen activated protein kinases (MAPKs) in the presence or absence of extracellular Ca(2+), being the cation clearly involved in the activation of neutrophils by fMLP. A strong correlation has been found between PKC isoforms, MAPKs and the selective physiological functions by [Delta(z)Leu(2)]-activated neutrophils. In a calcium-free condition, our data suggest that the failure of PKC beta1 translocation and of p38 MAPK phosphorylation by the analogue refers to its inability to induce chemotaxis, and that the failure by both fMLP-OMe and [Delta(z)Leu(2)] to evoke extracellular response kinase 1 and 2 (ERK1/2) phosphorylation would suggest a reduction in superoxide anion production.

Retrosulfonamido peptide analogues. Synthesis and crystal conformation of Boc-Pro-Leu-Ψ(NH-SO2)-Gly-NH2

Abstract Boc-Pro-Leu-Ψ(NH-SO 2 )-Gly-NH 2 ( 3 ) has been synthesized as the first example of a pseudopeptide incorporating the NH-SO 2 junction. The crystal structure of 3 indicates that the Ψ(NH-SO 2 ) induces a cisoidal (gauche − ) conformation which induces a backbone folding and prevents the H-bonded β-turn found in the parent peptide.

Two new formylated peptides able to activate chemotaxis and respiratory burst selectively as tools for studying human neutrophil responses

Two new For-Met-Leu-Phe-OH (FMLP) methyl ester analogues, For-Thp-Leu-Ain-OMe [Thp1, Ain3] and For-Met-delta zLeu-Phe-OMe [delta zLeu2], able to activate selectively chemotaxis and superoxide anion (O2-) release, respectively modulate intracellular cyclic AMP (cAMP) levels in different ways. FMLP and [delta zLeu2] enhance human neutrophil cAMP levels per se, and this effect is potentiated by Ro 201724, a non-xanthinic phosphodiesterase (PDE) inhibitor, whereas it is counteracted by 3-isobutyl-1-methyl-xanthine (IBMX), a blocker of both phosphodiesterase and adenosine receptors. In contrast, [Thp1, Ain3] is ineffective. However, no formylated peptides influence cAMP phosphodiesterase activity. Neutrophil preincubation with Ro 201724 or IBMX drastically reduces chemotaxis and superoxide anion (O2-) production triggered by peptides. Our results suggest that: (1) peptide-induced cAMP increase is probably indirect, and due mainly to the action on adenosine-sensitive adenylate cyclase; (2) formylated peptide, endowed solely with chemotactic activity is unable to increase neutrophil cAMP concentration; (3) cAMP elevation may represent a feed-back mechanism to inhibit the physiological responses induced by formylated peptides.

Selective acylations of aminophenols and hydroxyalkylphenols with 1-acetyl-v-triazolo[4,5-b]pyridine

Abstract The title triazolide serves as a convenient reagent for higly chemoselective acetylations of aminophenols and hydroxyalkylphenols.

A convenient one-pot procedure for the selective reduction of ketones in the presence of aldehydes

Abstract The title process has been accomplished by a three-step sequence involving protection of aldehyde as the imine, in situ reduction of ketone with lithium tri- tert -butoxyaluminohydride, and regeneration of aldehyde on hydrolytic work-up.

Synthesis and activity of HCO-Met-Leu-Phe-OMe analogues containing β-alanine or taurine at the central position

New synthetic analogues of the chemotactic N-formyltripeptide HCO-Met-Leu-Phe-OMe have been synthesized. The reported new models, namely Boc-Met-beta-Ala-Phe-OMe (1), HCO-Met-beta-Ala-Phe-OMe (2), Boc-Met-Tau-Phe-OMe (3), HCO-Met-Tau-Phe-OMe (4) and HCl.Met-Tau-Phe-OMe (5), are characterized by the presence at the central position of a residue of beta-alanine or 2-aminoethanesulfonic acid (taurine) replacing the native L-leucine. Whereas tripeptides 1 and 2 have been found quite inactive as chemoattractants, all the three models containing the Tau residue exhibit a remarkable activity. Superoxide anion production and lysozyme release have been also evaluated and the biological results are discussed together with the conformational preferences of the examined models.

For-Met-ΔzLeu-Phe-OMe: A new active analog of chemotactic N-formyltripeptides with β-turn crystal conformation

Abstract The title Δ z Leu containing N-formyltripeptide 2 , has been synthesized and found active in the superoxide production whereas inactive in the stimulation of human neutrophil migration. The X-ray crystallographic analysis reveals that 2 adopts a β-turn conformation stabilized by an intramolecular H-bond.

Water induced β-turn modification in a chemotactic tetrapeptide. Synthesis, crystal conformation, and activity of HCO-Met-Leu-ΔZPhe-Phe-OMe

In order to study the influence of the conformation on the activity and bioselectivity, the new tetrapeptide ligand of the chemotactic formylpeptide receptors HCO-Met-Leu-Δ Z Phe-Phe-OMe ( 2 ) has been studied. Compound 2 has been designed so as to induce a preferential β-turn conformation with the N -formyl group located outside the backbone loop. The crystallographic analysis reveals that 2 adopts only in part the expected conformation due to the presence of a water molecule isnide the turn. Details on the H-bonding network stabilizing the “open-turn” are given. The tetrapeptide 2 is active towards human neutrophils, stimulating directed migration, superoxide anion generation and lysozyme release. The influence of the backbone conformation on the bioselectivity is discussed.