Asymmetric Disulfides Research Articles

A unique and highly facile method for synthesising disulfide linked neoglycoconjugates: a new approach for remodelling of peptides and proteins

An asymmetric disulfide linkage, formed by conjugation of a 5-nitropyridine-2-sulfenyl activated thioglycoside and a protein or pre-assembled peptide sequence, represents a good structural mimic of natural asparagine glycosylation.

Heat-Induced Phase Separation of Self-Assembled Monolayers of a Fluorocarbon-Hydrocarbon Asymmetric Disulfide on a Au(111) Surface

Heat-induced phase separation of fluorocarbon-hydrocarbon self-assembled monolayers (SAMs) on a Au(111) surface was studied by scanning tunneling microscopy (STM), atomic force microscopy (AFM) and friction force microscopy (FFM). Phase-separated domains were depressed by 0.3 nm with a lateral dimension of 20–200 nm. The friction forces on the higher parts were smaller than those on the lower domains. The higher parts were assigned to the hydrocarbon chains, because the fluorocarbon chains should have a larger friction force acting on them than the hydrocarbon chains against the silicon nitride tip. Phase separation suggests cleavaging of the S–S bonds of disulfides in the SAMs. XPS measurements clearly showed an increase in the isolated Au–S binding species, suggesting the existence of the thiolate (monomer).

Quantum Interference Effects in Self-Assembled Asymmetric Disulfide Monolayers: Comparisons between Experiment and ab Initio/Monte Carlo Theories

Electron transfer measurements between solution redox probes and a Au electrode coated with self-assembled monolayers of symmetric and asymmetric ω-hydroxyalkane disulfides are used to probe the quantum interference between hydrocarbon chains of different lengths. While ab initio theory predicts a measurable destructive interference effect between hydrocarbon chains differing in length by a single methylene unit, electron transfer rates for the ferricyanide and horse heart cytochrome c are more consistent with rates estimated in the absence of the interference effect. The discrepancy between theory and experiment is discussed in light of possible interchain electronic coupling and phase segregation within the monolayers and limitations of the theoretical models.

Use of 2,2′-dithiobis(5-nitropyridine) for the heterodimerization of cysteine containing peptides. Introduction of the 5-nitro-2-pyridinesulfenyl group

2,2′-Dithiobis(5-nitropyridine) has proven to be a suitable reagent for the activation of the thiol function of cysteine in peptides and subsequent asymmetric disulfide formation. The utility of this reagent is tested in the preparation of de novo designed cytochrome model heterodimeric 62-mer peptides.

Synthesis of asymmetric disulfides as potential alternative substrates for trypanothione reductase and glutathione reductase: Part 2

The synthesis of asymmetrical disulfides, based on Zervas' inter-mediate, monocarbobenzoxy-L-cystine, has been developed. A series of substrate analogues of trypanothione disulfide (TSST) and glutathione disulfide (GSSG) are described, where the spermidine ring of (TSST) has been replaced by 3-dimethylaminopropylamine (DMAPA). The free amino group in Zervas' product was condensed with phenylalanyl, tryptophanyl or glutamyl residues, while the carbobenzoxy group was unaffected under the reaction conditions employed. The same synthetic approach was applied in the design of analogues of glutathione disulfide (GSSG).

Ultrathin self-assembled polymeric films on solid surfaces. III. Influence of acrylate dithioalkyl side chain length on polymeric monolayer formation on gold

Self-assembled films of acrylate polymers containing dithioalkyl side chains of varying lengths have been fabricated on gold substrates by adsorption from dilute organic solution. Anchoring alkyl side chain types studied include lipoate (n=4), pentyl dithioundecanoate (n=10), pentyl dithiopalmitate (n=15), and pentyl dithiotricosonate (n=22), where n represents the number of methylene units in the longer arm of the asymmetric disulfide side chain. Comprehensive characterization of polymer monolayers by x-ray photoelectron spectroscopy and reflection Fourier transform infrared spectroscopy showed improved order for structural assemblies of C11 (n=10) side chain polymer monolayers, over shorter and longer side chain polymer analogs, due to a higher percentage of bound thiolate anchors. Monolayer thicknesses range from 20 to 40 Å, primarily depending on side chain length and density along the polymer backbone. Cyclic voltammetry on gold electrodes shows that longer side chain polymer monolayers possess more structural defects resulting from considerable disorder in the films. Despite the less organized structural features for these polymer monolayers, their selective adsorption onto gold via specific side chain terminal disulfide anchors on microlithographed substrate patterns creates well-resolved surface-modified microstructures comparable to those from monomeric analogs, as shown by scanning Auger mapping.

Flavor production in tissue cultures of chive ( A. schoenoprasum L.): callus structure and flavor production

Allium species are an important source of natural flavourings for food and pharmaceutical preparations and have often been investigated in secondary metabolite studies. Tissue cultures of chive were initiated and subcultured for more than three years. Tissues producing organs and non-organogenetic tissues were examined for their structure and aroma compounds. The organ-generating ones developed root-like structures. Flavor production was investigated as sulfur volatile constituents and as amounts of enzymatically-produced pyruvic acid when tissues were crushed. Calli produced sulfur-containing flavor components, but less than fresh leaves. The main aroma component of fresh leaves was dipropyl disulfide, although asymmetric methyl and 1-propenyl disulfides were also present. The relative proportions of disulfides were modified in tissue cultures, with 1-propenyl disulfide being the main compound.

Interchain and intrachain crosslinking of actin thiols by a bifunctional thiol reagent

From 1,9-nonylenedithiol and Ellman's Reagent the bifunctional asymmetric disulfide n-nonylene-1,9-bis-[5-dithio-(2-nitrobenzoic acid)] (NBDN) was prepared. By monovalent reaction with cysteine-374 the crosslinker could be introduced into monomeric actin, with release of one equivalent of yellow 2-nitro-5-thiobenzoate (NTB). From the monovalent actin derivative we prepared a crosslinked actin dimer (Cys-374–Cys-374′) as well as a monomer with a crosslink between Cys-374 and Cys-10. Neither crosslinked actin species was able to polymerize the crosslinked monomer even in the presence of phalloidin. The crosslinked monomer polymerized on the addition of dithiothreitol, thus providing the first unpolymerizable actin species whose polymerizability can be restored under mild conditions. We suggest the use of NBDN as a thiol-specific crosslinker that reacts under spectrophotometric control and can be removed by the addition of thiols.

Intermolecular-directed reactivity in solid media. Radiogenic formation of phosphorus-centered radicals in chiral diphosphine disulfides studied by ESR

AWct Singlecrystal, powder, and frozen-matrix ESR experiments have been performed to study the radiogenic electron-capture properties of several diastereoisomeric and asymmetric diphosphine disulfides (R,RzP(S)P(S)R3R4). The principal values of the hyperfine couplings of several phosphorus-centered radical configurations are determined and related to the spin density distribution. Attention is focused on the strong differences in radiogenic properties, observed between the meso and racemic forms of phenyl- and tolyl-substituted diphosphine disulfides. The most striking result is that X irradiation of the crystalline meso compounds MePhP(S)P(S)MePh, Me@-Tol)P(S)P(S)Me@-Tol), and Ph(PhCHz)P(S)P(S)Ph(CH2Ph) does not lead to the formation of a three-electron bond PAP u* radical but invariably results in configurations in which the unpaired electron is primarily localized on one half of the molecule. X irradiation of the corresponding racemic forms, on the other hand, gives rise to PLP u* configurations. The observed discrimination between symmetric and asymmetric configurations is explained in terms of intermolecular steric interactions affecting the geometry relaxation of the precursor molecule after initial electron addition. For a quantitative assessment, the change in van der Waals energy resulting from elongation of the P-P bond of the molecules in their respective crystal lattices was calculated with X-ray crystallographic data. The calculations reveal significantly stronger steric interactions for the aromatic meso compounds than for their racemic forms, in agreement with the absence of PAP u* configurations in the first. X irradiation of diphosphine disulfides in a frozen THF matrix almost invariably results in a single radical product, being the PAP u* configuration, and differences between meso and racemic isomers disappear. This is a consequence of the fact that in a randomly oriented solid matrix the molecular packing is less tight than in a molecular crystal, making more space available to the precursor molecule. It is concluded that in case stabilization of the initial electron adduct via P-P bond length elongation is unfavorable because of steric interactions, other relaxation pathways become accessible, resulting in alternative phosphoranyl radical configurations. In recent years the radiochemistry of organophosphorus compounds has received considerable attention. The phosphoruscentered radicals, formed in the radiation process, are of special interest because of their diverse structural and dynamical prop erties and their possible relevance to radiation damage in biochemical systems.’” It has been shown from a number of single-crystal ESR studies that the precise nature of the configuration of a phosphoranyl radical depends on the type of ligands surrounding the central phosphorus nucleus. Only recently have effects other than the nature of the substituents been envisaged as being essential to the formation of radiogenic phosphoruscentered radicals. In this respect, aspects of conformation and configuration of the precursor molecules and the involvement of the precursor environment in the electron-capture process have been studied.4d Substituted diphosphine disulfides (R,R,P(S)P(S)R,R,) can serve as good probes to study phosphoranyl radical formation because of their intrinsic ability to adopt various radical configurations from a single molecule (Figure l).’ X irradiation of a diphosphine disulfide almost invariably results in the formation of an electron-capture radical in which the unpaired electron is accommodated in the antibonding u* orbital of the inter-phosphorus bond. As a consequence, the electron is symmetrically distributed over the two phosphorus nuclei. Complementary to this symmetrical PAP u* configuration, several radical structures with an asymmetrical spin density distribution have been established. One of the asymmetric structures frequently observed is a radical in which the odd electron is located in the vacant equatorial position of a trigonal-bipyramidal configuration (TBP-e). Another asymmetric structure has been identified as a phosphoranyl radical in which the unpaired electron resides in an antibonding u* orbital of the phosphorussulfur bond (PS U’).

An asymmetrical disulfide-containing photoreactive heterobifunctional reagent designed to introduce radioactive labeling into biological receptors

The synthesis of succinimido 1-amino-(4-azidosalicyloyl)-3,4-dithio-5-carboxylate, a heterobifunctional photoaffinity labeling reagent, is described. The cross-linker possesses an asymmetrical disulfide bond, and a general method for generating a spacer arm bearing an asymmetrical or symmetrical disulfide bond is detailed. The heterobifunctional reagent has been obtained in a minimum of steps and intermediates have been characterized. It is further shown that the reagent can be trace-labeled with [125I]-iodine and it has been used to modify phytohemagglutinin, a model protein. Upon irradiation, polymeric phytohemagglutinin derivatives are produced, as evidenced by electrophoretic analysis.

Interchange reaction of disulfides and denaturation of oxytocin by copper(II)/ascorbic acid/O 2 system

The interchange reaction of disulfides was caused by the copper(II)/ascorbic acid/O 2 system. The incubation of two symmetric disulfides, L-cystinyl-bis-L-phenylalanine (PP) and L-cystinyl-bis-L-tyrosine (TT), with L-ascorbic acid and CuSO 4 in potassium phosphate buffer (pH 7.2, 50 mM) resulted in the formation of an asymmetric disulfide, L-cystinyl-L-phenylalanine-L-tyrosine (PT), and the final ratio of PP:PT:TT was 1:2:1. As the reaction was inhibited by catalase and DMSO only at the initial time, hydroxyl radical generated by the copper (II)/ascorbic acid/O 2 system seemed to be responsible for the initiation of the reaction. Oxytocin and insulin were denatured by this system, and catalase and DMSO similaly inhibited these denaturations. As the composition of amino acids was unchanged after the reaction, hydroxyl radical was thought to cause the cleavage and/or interchange reaction of disulfides to denature the peptides.

ChemInform Abstract: MELANOTROPIN RECEPTORS. II. SYNTHESIS AND BIOLOGICAL ACTIVITY OF α‐MELANOTROPIN/TOBACCO MOSAIC VIRUS DISULFIDE CONJUGATES

AbstractAsymm. Disulfid‐Konjugate von Mercaptosuccinyl‐Tabakmosaikvirus (TMV∼SH) mit dem α‐Melanotropin (Ia) (α‐MSH‐Analogen (Id) werden über das S‐Sulfoderivat (Ic) [zugänglich aus (Ib)] dargestellt.

ChemInform Abstract: SYNTHESIS OF FRAGMENTS OF ARGININE VASOPRESSIN AND OXYTOCIN CONTAINING A CYSTINE RESIDUE IN POSITION 6

AbstractDie Synthese der Titelverbindungen (VI), (VII), (XIa), (Xlc) (Arginin‐Vasopressin‐Fragmente) bzw. (IX), (XIb), (Xld) (Oxytocin‐Frag‐ mente) wird beschrieben.

Synthesis of fragments of arginine vasopressin and oxytocin containing a cystine residue in position 6

AbstractThe synthesis is described of several fragments of the neurohypophyseal nonapeptide hormones arginine vasopressin and oxytocin. One group of fragments is characterized by the presence of an asymmetrical disulfide (a cystine residue in position 6), a second group consists of dimeric (symmetrical disulfides) fragments.As common intermediates, peptides containing an S‐tritylcysteine residue were synthesized by the fragment condensation approach. Treatment with methoxycarbonylsulfenyl chloride followed by reaction with the free thiol function of cysteine gave the asymmetrical disulfides, while treatment of the S‐tritylcysteine containing peptide with iodine resulted in the corresponding dimers. Peptides with an N‐terminal glutamine residue (position 4) were found to convert spontaneously into the corresponding pyroglutamic acid products.

Angiotensin II Analogues. Part II. Synthesis and incorporation of the sulfur‐containing aromatic amino acids: L‐(4′‐SH)Phe, L‐(4′‐SO2NH2)Phe, L‐(4′‐SO)Phe and L‐(4′‐S‐CH3)Phe

AbstractL‐Phenylalanine has been treated with chlorosulfonic acid and the product was either hydrolyzed, ammonolyzed or reduced. The resulting sulfonic‐acid and aminosulfonyl derivatives have been employed for peptide synthesis with Boc‐protection of the Nα‐position only. The reduction product L‐(4′‐SH)Phe has been protected by formation of asymmetric disulfides or with various thiol protecting groups (benzyl‐, methyl‐ and acetamidomethyl groups, the latter being the most suitable for peptide synthesis).With these protected amino acids several analogues of angiotensin II have been synthesized by the solid‐phase method. These analogues have been used for structure‐activity relationship studies on three different bioassays.

Gold(III) catalyzed oxidation of sulfides to sulfoxides by nitric acid under phase-transfer conditions: a new synthesis of sulfoxides

Gold(III) halides catalyze the oxidation of sulfides to sulfoxides in a phase-transfer process. The organic sulfides, dissolved in nitromethane, are treated with (Bu 4N +AuCl 4 −) in catalytic amount and aqueous nitric acid which acts as oxidant. The oxidation of the thio-group is selective and can be carried out also in the presence of other oxidizable groups, such as vinyl, tertiary amino, hydroxy, diol etc, which are left unchanged. Moreover in the case of asymmetric disulfides the reaction is regiospecific leading to the formation of a single monosulfoxide.

Cystinuria therapy by ascorbic acid (author's transl)

At the beginning of the four chapters on phenomena, analysis, pathophysiology and therapy of cystinuria the essentials of the published literature are summarized. The frequency of cystinuria is in the order of 1:10,000. Besides the cystine lithiasis occurring in nine tenths of all cystinuria patients neurological diseases may also be observed. All commonly applied methods to analyze cystine detect the sum of cystine and cysteine. Cystinuria is characterized by a higher cystine excretion, up to the 100-fold of the normal. Also the concentrations of lysine, arginine and ornithine in the urine of cystinuria patients are elevated, caused by intestinal and renal transport defects. Inevitable damage of renal parenchyma by multiple operations can drastically be reduced by the therapy with D-penicillamine or alpha-mercaptopropionylglycine. The disadvantages of that formation of soluble asymmetric disulfides are the side effects, such as nausea, gastric difficulties and dermatosis, occurring in up to 50% of the patients. Using the especially developed method with HPLC separation and electrochemical detector with a mercury electrode, cystine and cysteine are analyzed simultaneously. In the urine of healthy persons the molar concentration of cysteine is in the same order as cystine. But in cystinuria the cysteine concentration in urine is about a thousand times less than that of cystine. These results are evidence that a shifted redox-equilibrium of cystine-cysteine is also typical of cystinuria. The molar cysteine percentage of cysteine in healthy persons is increased from 30 to 50% by oral ascorbic acid administration. Therefore a vitamin C therapy for cystinuria is developed. 31 cystinuria patients who receive 5 g of vitamin C a day show a decrease in the cystine concentration of about 40%. Up to now, no side effects have been observed. The most obvious sign of the positive effect of the proposed vitamin C therapy for cystinuria is the missing cystine sediment in fresh urine.

51] Assays for differentiation of glutathione S-Transferases

Publisher Summary This chapter provides the spectrophotometric, titrimetric, nitrite, and cyanide assay for the differentiation of glutathione S-transferases. Spectrophotometric assays depend upon a direct change in the absorbance of the substrate when it is conjugated with glutathione (GSH). Because each of the reactions is catalyzed at a finite rate in the absence of enzyme, care is needed to reduce nonenzymatic catalysis by minimizing substrate concentrations and by decreasing pH wherever necessary. Titrimetric assay is based on the principle that the conjugation of alkyl halides with GSH can be measured titrimetrically. Although acid production accompanies many of the transferase catalyzed reactions in which thioethers are formed, titrimetry is only used when more convenient assays are not available. Nitrite assay is based on the principle that nitrite is released when GSH reacts with nitroalkanes or with organic nitrate esters. The nitrite can be assayed as the limiting factor in a diazotization reaction with sulfanilamide that produces a readily quantitatable pink dye. Cyanide assay is based on the fact that when glutathione transferases catalyze the attack of the glutathione thiolate ion on the electrophilic sulfur atom of several organic thiocyanates, it results in the formation of an asymmetric glutathionyl disulfide and cyanide. Cyanide can be readily quantitated by a calorimetric method.

New synthesis of somatostatin according to the S-tert-butylthiocysteine procedure.

AbstractTo exemplify the usefulness of the S‐tert‐butylthio group for a reversible blocking of the cysteine thiol function in peptide synthesis, fully protected dihydrosomatostatin was prepared by the fragment‐condensation procedure. The experimental results confirm the excellent stability of the asymmetric disulfide under the normal conditions of peptide synthesis and prove that the selective, acid‐catalyzed nucleophil removal—as well as by mercaptans—of the 2‐nitrophenylsulfenyl group proceeds smoothly in the presence of this thiol protection. Thus, the strategy of overall acid‐labile side‐chain protection in combination with the Nα‐2‐nitrophenylsulfenyl group for the chain‐elongation steps can be successfully applied to the synthesis of cysteine‐containing peptides using their S‐tert‐butylthio derivatives. Removal of the acid‐labile groups, followed by reductive cleavage of the asymmetric disulfides and successive air oxidation, allowed a clean conversion of protected dihydrosomatostatin into somatostatin at a high degree of purity and in good yields.

ChemInform Abstract: THE PREPARATION AND OXIDATION OF DISULFIDES AS A ROUTE TO SULFONE‐SULFIDES

AbstractBei der Darstellung von Disulfiden in alkoxidhaltigem Milieu wird die Bildung von Alkoxyderivaten als Konkurrenzreaktion beobachtet.