Alessandra Spirito

Synthesis and biological evaluation of a novel pyroglutamyl-modified TRH analogue

The TRH analogue 3, incorporating the (S)-isothiazolidine-1,1-dioxide-3-carboxylic acid (1) moiety in place of the native L-pyroglutamic acid (pGlu) residue, has been synthesized and fully characterized by 1H and 13C NMR. The effects of replacing pGlu with its sulphonamido counterpart on biological activity have been investigated. This peptide, which is significantly stabilized towards hydrolysis by pyroglutamyl peptidase type I (PP I, EC 3.4.19.3), has shown to maintain in vitro prolactin-releasing activity.

Ψ(SO2NH) transition state isosteres of peptides. Synthesis and bioactivity of sulfonamido pseudopeptides related to carnosine

This paper reports the synthesis of tauryl dipeptides related to carnosine. In particular H-Tau-His-OH (5), H-Tau-His(pi-Me)-OH (6) and H-Tau-His(tau-Me)-OH (9) are described. The enzyme carnosinase has been isolated from pig kidney and after purification has been used to test the stability and the inhibitory activity of the three new analogues. H-Tau-His-OH (5) and H-Tau-His(tau-Me)-OH (9) were found to possess weak inhibitory properties towards carnosinase, while H-Tau-His(pi-Me)-OH (6) proved to be devoid of any significant activity. All the three sulfonamido pseudopeptides 5, 6 and 9 show stability to carnosinase activity.

Proline-glutamate chimeras in isopeptides. Synthesis and biological evaluation of conformationally restricted glutathione analogues.

The two novel diastereoisomeric glutathione analogues 1 and 2 have been designed and synthesized by replacing the native gamma-glutamylic moiety with the conformational rigid skeleton of cis- or trans-4-carboxy-L-proline residue. Both analogues have been obtained by following the solution phase peptide chemistry methodologies and final reduction of the corresponding disulfide forms 13 and 14. The two analogues 1 and 2 have been tested towards gamma-glutamyltranspeptidase (gamma-GT) and human glutathione S-transferase (hGST P1-1). Both analogues 1 and 2 are completely resistant to enzymatic degradation by gamma-GT. The S-transferase utilizes the analogue 2 as a good substrate while is unable to bind the analogue 1.

Hypotaurine protection on cell damage by singlet oxygen.

Singlet oxygen (1O2), generated by irradiating methylene blue, is toxic to melanoma cell cultures. Hypotaurine is known to scavenge efficiently singlet oxygen; the addition of hypotaurine (800 microM) to the medium during irradiation of the dye produces a greater protective effect on cells than taurine added at the same concentration. The assay of some detoxifying enzymatic activities indicate a different mechanism of protection of the two molecules: taurine induces an efficient detoxifying enzymatic action with respect to the control; hypotaurine exerts its effect greatly by specifically scavenging singlet oxygen.

Hypotaurine Oxidation: An HPLC-Mass Approach

Hypotaurine reacts with various reactive oxygen species, although mainly with hydroxyl radicals. The compound bis-aminoethyl-α-disulfone (H2N-CH2-CH2-SO2-SO2-CH2-CH2-NH2) has been proposed as one of the intermediate products during the ultraviolet light-catalyzed oxidation of hypotaurine13. The disulfone has been proposed as a product of the hydroxyl radical quenching activity of hypotaurine6 and has been demonstrated to be present in vitro after hypotaurine oxidation by Fenton’s reagent or in the presence of enzymatically-generated hydroxyl radicals7. The sulfonyl radical RSO2· has been hypothesized as a reaction intermediate6,7. In an attempt to understand in more detail the reaction of hypotaurine with Fenton’s reagent, we studied this reaction by LC/APCI-MS which evaluates the time course of product formation and the production of intermediates. The presence of bis-aminoethyl-α-disulfone among the reaction products could not be demonstrated by this technique. Attempts to synthesize this compound by reported methods for the synthesis of other α-disulfones or by reaction involving chemically- or enzymatically-generated hydroxyl radicals were also unsuccessful.

Hypotaurine Protection on Cell Damage by H2O2 and on Protein Oxidation by Cu++ and H2O2

The antioxidant activity of hypotaurine on cell structure has primarily been studied utilizing artificial liposomes and isolated lipoproteins18. Most studies with whole cells have utilized sperm cells to study the effect of oxidative stress on cellular function in the presence of varying concentrations of hypotaurine1,4,11,14,19. In this paper we will report experiments performed using two in vitro model systems.

Synthesis and biological evaluation of the disulfide form of the glutathione analogue γ-(L-glutamyl)-L-cysteinyl-L-aspartyl-L-cysteine

By using the chain to chain mode of cyclization the title glutathione analogue (4), containing the 11-membered disulfide ring replacing the native -Cys-Gly fragment, has been synthesized and characterized together with its reduced dithiol form gamma-Glu-Cys-Asp-Cys (5). The activity of (4) with gamma-glutamyl-transferase and glutathione reductase has been evaluated and compared with those of the two conformationally restricted glutathione analogues (2) and (3) previously reported.

Hypotaurine disproportionation reaction: Identification of products

SummaryHypotaurine, concentrated under reduced pressure in HCl solution, partially (30–40%) degrades into taurine (about 30%), 2-aminoethyl-2-aminoethanethiolsulfonate (about 10%) and ethanolamine. The degradation products were identified using LC/APCI-MS, NMR, amino acid analysis and various chromatographics. The identities were confirmed by comparing the HPLS, MS and NMR characteristics of authentic compounds. One of the degradation processes during concentration of HCl solution of hypotaurine is therefore a disproportionation reaction which can interfere with the experimental results, when studying hypotaurine in biological systems.