4-Amino-1,2-dithiolane-4-carboxylic acid (Adt) as cysteine conformationally restricted analogue. Synthetic protocol for Adt containing peptides

Asparagusic Acid - A Unique Approach toward Effective Cellular Uptake of Therapeutics: Application, Biological Targets, and Chemical Properties

The synthetic approaches towards unique asparagusic acid and its analogues as well as its chemical use, the breadth of its biological properties and their relevant applications have been explored. The significance of the 1,2-dithiolane ring tension in dithiol-mediated uptake and its use for the intracellular transport of molecular cargoes is discussed alongside some of the challenges that arise from the fast thiolate-disulfide interchange. The short overview with the indication of the available literature on natural 1,2-dithiolanes synthesis and biological activities is also included. The general review structure is based on the time-line perspective of the application of asparagusic acid moiety as well as its primitive derivatives (4-amino-1,2-dithiolane-4-carboxylic acid and 4-methyl-1,2-dithiolane-4-carboxilic acid) used in clinics/cosmetics, focusing on the recent research in this area and including international patents applications.

Enhanced Photocatalytic Hydrogen Production by Hybrid Streptavidin-Diiron Catalysts

Hybrid protein-organometallic catalysts are being explored for selective catalysis of a number of reactions, because they utilize the complementary strengths of proteins and of organometallic complex. Herein, we present an artificial hydrogenase, StrepH2, built by incorporating a biotinylated [Fe-Fe] hydrogenase organometallic mimic within streptavidin. This strategy takes advantage of the remarkable strength and specificity of biotin-streptavidin recognition, which drives quantitative incorporation of the biotinylated diironhexacarbonyl center into streptavidin, as confirmed by UV/Vis spectroscopy and X-ray crystallography. FTIR spectra of StrepH2 show characteristic peaks at shift values indicative of interactions between the catalyst and the protein scaffold. StrepH2 catalyzes proton reduction to hydrogen in aqueous media during photo- and electrocatalysis. Under photocatalytic conditions, the protein-embedded catalyst shows enhanced efficiency and prolonged activity compared to the isolated catalyst. Transient absorption spectroscopy data suggest a mechanism for the observed increase in activity underpinned by an observed longer lifetime for the catalytic species Fe^I Fe⁰ when incorporated within streptavidin compared to the biotinylated catalyst in solution.

Construction of sulfur-containing moieties in the total synthesis of natural products

This review surveys the total syntheses of sulfur-containing natural products where sulfur atoms are introduced with different sulfurization agents to construct related sulfur-containing moieties.

Peptide flatlandia: a new-concept peptide for positioning of electroactive probes in proximity to a metal surface

A helical hexapeptide was designed to link in a rigid parallel orientation to a gold surface. The peptide sequence of the newly synthesized compound is characterized by the presence of two 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) residues (positions 1 and 4) to promote a bidentate interaction with the gold surface, two L-Ala residues (positions 2 and 5) and two-aminoisobutyric acid (Aib) residues (positions 3 and 6) to favor a high population of the 310-helix conformation. Furthermore, a ferrocenoyl (Fc) probe was inserted at the N-terminus to investigate the electronic conduction properties of the peptide. X-Ray photoelectron spectroscopy and scanning tunneling microscopy techniques were used to characterize the binding of the peptide to the gold surface and the morphology of the peptide layer, respectively. Several electrochemical (cyclic voltammetry, chronoamperometry, square wave voltammetry) techniques were applied to analyze the electrochemical activity of the Fc probe, along with the influence of the peptide 3D-structure and the peptide layer morphology on electron transfer processes.

No selenium required: reactions catalyzed by mammalian thioredoxin reductase that are independent of a selenocysteine residue

Mammalian thioredoxin reductase (TR) contains a rare selenocysteine (Sec) residue in a conserved redox-active tetrapeptide of sequence Gly-Cys(1)-Sec(2)-Gly. The high chemical reactivity of the Sec residue is thought to confer broad substrate specificity to the enzyme. In addition to utilizing thioredoxin (Trx) as a substrate, other substrates are protein disulfide isomerase, glutaredoxin, glutathione peroxidase, NK-lysin/granulysin, HIV Tat protein, H(2)O(2), lipid hydroperoxides, vitamin K, ubiquinone, juglone, ninhydrin, alloxan, dehydroascorbate, DTNB, lipoic acid/lipoamide, S-nitrosoglutathione, selenodiglutathione, selenite, methylseleninate, and selenocystine. Here we show that the Cys(2) mutant enzyme or the N-terminal reaction center alone can reduce Se-containing substrates selenocystine and selenite with only slightly less activity than the wild-type enzyme, in stark contrast to when Trx is used as the substrate when the enzyme suffers a 175-550-fold reduction in k(cat). Our data support the use of alternative mechanistic pathways for the Se-containing substrates that bypass a critical ring-forming step when Trx is the substrate. We also show that lipoic acid can be reduced through a Sec-independent mechanism that involves the N-terminal reaction center. These results show that the broad substrate specificity of the mammalian enzyme is not due to the presence of the rare Sec residue but is due to the catalytic power of the N-terminal reaction center. We hypothesize that the N-terminal reaction center can reduce substrates (i) with good leaving groups such as DTNB, (ii) that are highly electrophilic such as selenite, or (iii) that are activated by strain such as lipoic acid/lipoamide. We also show that the absence of Sec only changed the IC(50) for aurothioglucose by a factor of 1.7 in the full-length mammalian enzyme (83-142 nM), but surprisingly the truncated enzyme showed much stronger inhibition (25 nM). This contrasts with auranofin, where the absence of Sec more strongly perturbed inhibition.

Peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt): conformation of Boc-Adt-Adt-NHMe and NH...S interactions

To study the conformational preferences induced by the insertion of the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) residue into a peptide backbone, the achiral N-protected dipeptide methylamide Boc-Adt-Adt-NHMe (1) was synthesized and its crystal state and solution conformation studied and compared with that exhibited by its carba-analogue Boc-Ac5c-Ac5c-NHMe containing two residues of 1-aminocyclopentane-1-carboxylic acid (Ac5c). Compound 1 in the crystal adopts a type-III beta-turn conformation and an analogous structure is that preferred in chloroform solution as established by 1H-NMR and NOE information. In the crystal packing three different Adt rings form a cavity and the involved sulphur atoms give rise to unusual multiple interactions with one NH group. The chemical nature of these intermolecular and intramolecular main-chain...side-chain NH...S interactions are discussed in terms of quantum chemical calculations.

Synthesis and activity of novel glutathione analogues containing an urethane backbone linkage

The new GSH analogues H-Glo(-Ser-Gly-OH)-OH (5), its O-benzyl derivative 4, and H-Glo(-Asp-Gly-OH)-OH (9), characterized by the replacement of central cysteine with either serine or aspartic acid, and containing an urethanic fragment as isosteric substitution of the scissile gamma-glutamylic junction, have been synthesized and characterized. Their ability to inhibit human GST P1-1 (hGST P1-1) in comparison with H-Glu(-Ser-Gly-OH)-OH and H-Glu(-Asp-Gly-OH)-OH, which are potent competitive inhibitors of rat GST 3-3 and 4-4, has been evaluated. In order to further investigate the effect of the isosteric substitution on the binding abilities of the new GSH analogues 4, 5 and 9, the previously reported cysteinyl-containing analogue H-Glo(-Cys-Gly-OH)-OH has been also evaluated as a co-substrate for hGSTP1-1.

Peptide backbone folding induced by the C(alpha)-tetrasubstituted cyclic alpha-amino acids 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) and 1-aminocyclopentane-1-carboxylic acid (Ac5c). A joint computational and experimental study

The conformational study of a new group of synthetic peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt), a cysteine-related achiral residue, has been carried out through a joint application of computational and experimental methodologies. Molecular Dynamics simulations clearly suggest the tendency of this molecule to adopt a gamma-turn conformation in vacuum and help in analyzing the complex and crucial conformational behaviour of the dithiolane ring which appears to preferentially adopt a C(S)-like structure. Electronic structure calculations carried out in solution using the Density Functional Theory also indicate the preservation of the gamma-like folding in apolar solvents and the helix-like one in more polar solvents. A comparison with the achiral 1-aminocycloalkane-1-carboxylic acid (Ac5c) has been carried out using the same computational tools. NMR and IR data on dipeptide derivatives containing the Adt or Ac5c residue show that in chloroform solution all the models prefer a gamma-turn structure, centered at the cyclic residue, stabilized by an intramolecular H-bond, whereas in a more polar solvent, i.e. dimethyl sulfoxide, this folding is not maintained. The experimental conformational studies, extended to N-Boc protected tripeptides, clearly indicate the remarkable tendency of both the five-membered C(alpha)-tetrasubstituted cyclic amino acids Adt and Ac5c to induce the gamma-turn structure also in models able to adopt the beta-bend conformation.

Synthesis and biological evaluation of the disulfide form of the glutathione analogue gamma-(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.

Synthesis of 1,2-dithiolane analogues of leucine for potential use in peptide chemistry

[reaction: see text]1,2-Dithiolanes present several points of interest for both peptide and medicinal chemistry, yet no chiral alpha-amino acids containing this five-membered heterocyclic system are available. We report here the first synthesis of N- and C-protected derivative of (S)-2-amino-3-(1,2-dithiolan-4-yl)propionic acid (Adp) and its 1,3-dithiolic form.

Exploring the interest of 1,2-dithiolane ring system in peptide chemistry. Synthesis of a chemotactic tripeptide and x-ray crystal structure of a 4-amino-1,2-dithiolane-4-carboxylic acid derivative

Due to their relevant biological functions and specific chemical reactivity 1,2-dithiolanes (five-membered cyclic disulfides) represent an emerging class of heterocyclic compounds. However, despite the extensive research centered on lipoic acid and its analogues, only very few data are at the present available on peptides containing this ring system. We report here synthesis, conformation and bioactivity of a fMLF-OMe analogue, namely For-Met-Adt-Phe-OMe (7), in which the residue of the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) (4) replaces the central L-leucine. The crystal conformation of the synthetic intermediate Boc-Adt-OMe (5) is also described and compared to that of lipoic acid (R-1,2-dithiolane-3-pentanoic acid) (3) and asparagusic acid (1,2-dithiolane-4-carboxylic acid) (2).