Vincenzo Rizzo

Synthesis and evaluation of new elastase inhibitors. I. 1,1-Dioxocephem-4-thiolesters

Several 7α-chloro and 7α-methoxy cephalosporin thiolester sulphones variously substituted at the C-3′ position were synthesized from 7-amino-3-deacetoxycephalosporanic acid (7-ADCA). The compounds are time-dependent inhibitors of human leukocyte elastase (HLE) with effective Ki ranging from micro- to nanomolar values, and second order rate constant reaching 106 M−1s−1; they also inhibit porcine pancreatic elastase with similar, though not identical efficiency. Compared to the corresponding cephem esters, the thiolesters of the 7-Cl series inhibit HLE up to 10 times as fast. Complete enzyme inactivation is achieved when a leaving group at C-3′ (OAc or S-Het) is present, at the expense however of stability towards hydrolytic β-lactam cleavage. In the 7-OMe series the thiolester compounds are far more stable and retain good efficiency for irreversible enzyme inhibition, superior to that displayed by the corresponding ester compounds. Three representative compounds (including one ester and two thiolesters) are shown to be effective inhibitors of HLE in the presence of insoluble elastin.

A comparative study of low-density lipoprotein interaction with glycosaminoglycans.

The association between low-density lipoprotein (LDL) and a series of well characterized dermatan and chondroitin sulfates has been investigated by means of the fluorescence anisotropy technique with competition experiments using a fluorescein-labeled high LDL-affinity heparin fraction as a reference. Preparations of glycosaminoglycan (GAG) with sulfation degrees varying over a wide range, as obtained by fractionation or by chemical modification, were chosen for this study. The influence of chain length, which had been found sizeable in a former study of heparin affinity for LDL, was taken into account with an empirical correction of dissociation constants. After this correction, a linear relationship was found between the logarithm of dissociation constants and the number of sulfate groups per disaccharide unit, ns, both for dermatan and chondroitin sulfates, and for heparins. At comparable ns values, however, dermatan sulfates and heparins, which contain L-iduronic acid in their backbone, show higher LDL-affinity than chondroitin sulfates, which contain only D-glucuronic acid. Though confirming a non-specific, predominantly electrostatic interaction between GAGs and LDL, these results indicate modulation of LDL affinity by the polysaccharide backbone.

Co-oligopeptides of glycine and aromatic amino acids with variable distance between the aromatic residues. IV. Spectroscopic properties of tryptophan-containing peptides in a cyclohexane phase.

L-Tryptophan, L-tryptophanylglycine, glycyl-L-tryptophan, glycyl-L-tryptophanylglycine and glycyl-L-tryptophanylglycylglycyl-L-tryptophanylglycine have been transferred from an aqueous solution (generally 0.1 M NaOH) to cyclohexane, using the quaternary ammonium salt trioctylmethyl ammonium chloride (NR+4Cl-, soluble in cyclohexane but not in water) as the transporting agent. The spectroscopic properties of L-tryptophan and tryptophan-containing peptides have been studied in the cyclohexane phase. With respect to the aqueous solutions, ultraviolet absorption spectra are characterized by a considerable red shift of the absorption maxima and by a hypochromicity of up to 10%. Fluorescence spectra generally show emission maxima which are characteristic of polar environments, accompanied by a significant enhancement of the quantum yield. CD spectra have also been investigated for all peptides and compared with those for aqueous systems reported in preceding publications. All these spectral changes cannot be attributed solely to the cyclohexane solvent effect. It is suggested that these anomalous spectral properties of the tryptophan-containing compounds in the cyclohexane-NR+4 solution are due to the influence the electrostatic field of the ion pair has on the indole chromophore. The possible implications of this finding for the spectroscopic properties of aromatic residues buried in the polar interior of proteins are discussed.