Radiation chemistry of a multicomponent aqueous system relevant to chemistry of cometary nuclei

Summary We have examined a water-dominated multicomponent system after irradiation in the multimegarad dose range with gamma rays from a⁶⁰Co source at both 77 and 310 K. The constituents were simple organic compounds in the proportions in which they appear in a dense interstellar cloud: HCN/CH₃OH/CH₃CN/C₂H₅CN/HCOOH=10.60.20.10.05. The total amounts were adjusted to correspond to a carbon to nitrogen ratio of 1.8 and a water content of about 50% in a cometary nucleus where the dust to volatiles ratio is 1; the total amount of CN-bearing compounds was taken to correspond to 0.4% of the cometary mass. In experiments at 310 K about 40 radiolytic products are identified, among them aldehydes and amino and carboxylic acids. Abundant polymeric material (M_w up to 80,000 daltons) is formed. The basic aspects of radiolysis of the liquid system are present also at 77 K, although at radiation-chemical yields that are lower by one to two orders of magnitude. We have considered the relevance of the present findings to the chemistry of a liquid-water core and the icy layers of a cometary nucleus.     

Type and concentration of redox reagents influencing nitrile formation upon myrosinase (Brassica carinata)-catalyzed hydrolysis of glucosibarin

The ratio of isothiocyanates (ITCs) to nitriles formed in the myrosinase-catalyzed hydrolysis of glucosinolates is a key factor determining the physiological effect of glucosinolate containing plants and materials. In this context, the mechanism by which nitrile formation occurs is not well understood. In the present paper we have studied the effect of three redox reagents – Fe²⁺, glutathione (GSH) and ascorbic acid – on the profile of products obtained upon the hydrolysis of a model glucosinolate (glucosibarin ((2R)-2-hydroxy-2-phenylethylglucosinolate)) catalyzed by Brassica carinata myrosinase. A Micellar Electrokinetic Capillary Chromatography method that allows following on-line the hydrolysis of the glucosinolate, the formation of the degradation products and the oxidation of GSH was used. Increasing the concentration of Fe²⁺ and GSH (from 0.25- to 2-fold molar excess with respect to the glucosinolate) increased the ratio of nitrile ((2R)-2-hydroxy-2-phenylethylcyanide) to oxazolidine-2-thione ((5S)-5-phenyloxazolidine-2-thione), whereas increasing the concentration of ascorbic acid decreased this ratio. Low concentrations of ascorbic acid favored nitrile formation. A mechanism for nitrile formation involving a disulfide bond in the myrosinase complex is proposed.     

The current and future applications of microorganism in the bioremediation of cyanide contamination

Inorganic cyanide and nitrile compounds are distributed widely in the environment, chiefly as a result of anthropogenic activity but also through cyanide synthesis by a range of organisms including higher plants, fungi and bacteria. The major source of cyanide in soil and water is through the discharge of effluents containing a variety of inorganic cyanide and nitriles. Here the fate of cyanide compounds in soil and water is reviewed, identifying those factors that affect their persistence and which determine whether they are amenable to biological degradation. The exploitation of cyanides by a variety of taxa, as a mechanism to avoid predation or to inhibit competitors has led to the evolution in many organisms of enzymes that catalyse degradation of a range of cyanide compounds. Microorganisms expressing pathways involved in cyanide degradation are briefly reviewed and the current applications of bacteria and fungi in the biodegradation of cyanide contamination in the field are discussed. Finally, recent advances that offer an insight into the potential of microbial systems for the bioremediation of cyanide compounds under a range of environmental conditions are identified, and the future potential of these technologies for the treatment of cyanide pollution is discussed.     

Regioselective addition of bifunctional oximehydroxamic acid by the hydroxamic group to Pt(IV)-coordinated nitriles

The metal-mediated coupling between the nitriles RCN in the platinum(IV) complexes trans-[PtCl₄(RCN)₂] (RMe, Et, CH₂Ph, Ph), cis/trans-[PtCl₄(MeCN)(Me₂SO)] and the newly synthesized bifunctional oximehydroxamic acid, viz. N,2-dihydroxy-5-(1-hydroxyiminoethyl)benzamide, proceeds smoothly in CH₂Cl₂ at 40-45 °C to accomplish the new metallaligands HNC(R)ONHC(O)C₆H₃(2-OH)(5-C(Me)NOH) with pendant oxime functionalities due to the regioselective addition of the reagent via its hydroxamic groups. The obtained iminoligands exist in hydroxamic/hydroximic tautomeric equilibrium in solution. The structures of the isolated compounds are based on elemental analyses (C, H, N), IR, 1D ¹H, ¹³C{¹H}, and 2D NMR correlation experiments, i.e. ¹H,¹³C-COSY, ¹H,¹³C long range COSY, ¹H,¹⁵N-COSY, and ¹H,¹⁵N long range COSY.     

N-Sulfonyl dipeptide nitriles as inhibitors of human cathepsin S: In silico design,synthesis and biochemical characterization

A library of cathepsin S inhibitors of the dipeptide nitrile chemotype, bearing a bioisosteric sulfonamide moiety, was synthesized. Kinetic investigations were performed at four human cysteine proteases, i.e. cathepsins S, B, K and L. Compound 12 with a terminal 3-biphenyl sulfonamide substituent was the most potent (K_i = 4.02 nM; selectivity ratio cathepsin S/K = 5.8; S/L = 67) and 24 with a 4′-fluoro-4-biphenyl sulfonamide substituent the most selective cathepsin S inhibitor (K_i = 35.5 nM; selectivity ratio cathepsin S/K = 57; S/L = 31). In silico design and biochemical evaluation emphasized the impact of the sulfonamide linkage on selectivity and a possible switch of P2 and P3 substituents with respect to the occupation of the corresponding binding sites of cathepsin S.     

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent reactions with azides to form cyanocarbene intermediates. The synthesis of hypervalent iodonium alkynyl triflates can be facile, but difficulties stem from their isolation and reactivity. In particular, the necessity to use filtration under inert atmosphere at -45 °C for some HIATs requires special care and equipment. Once isolated, the compounds can be stored and used in reactions with azides to form cyanocarbene intermediates. The evidence for cyanocarbene generation is shown by visible extrusion of dinitrogen as well as the characterization of products that occur from O-H insertion, sulfoxide complexation, and cyclopropanation. A side reaction of the cyanocarbene formation is the generation of a vinylidene-carbene and the conditions to control this process are discussed. There is also potential to form a hypervalent iodonium alkenyl triflate and the means of isolation and control of its generation are provided. The O-H insertion reaction involves using a HIAT, sodium azide or tetrabutylammonium azide, and methanol as solvent/substrate. The sulfoxide complexation reaction uses a HIAT, sodium azide or tetrabutylammonium azide, and dimethyl sulfoxide as solvent. The cyclopropanations can be performed with or without the use of solvent. The azide source must be tetrabutylammonium azide and the substrate shown is styrene.     

Insights into catalytic activity of industrial enzyme Co-nitrile hydratase. Docking studies of nitriles and amides

Nitrile hydratase (NHase) is an enzyme containing non-corrin Co³⁺ in the non-standard active site. NHases from Pseudonocardia thermophila JCM 3095 catalyse hydration of nitriles to corresponding amides. The efficiency of the enzyme is 100 times higher for aliphatic nitriles then aromatic ones. In order to understand better this selectivity dockings of a series of aliphatic and aromatic nitriles and related amides into a model protein based on an X-ray structure were performed. Substantial differences in binding modes were observed, showing better conformational freedom of aliphatic compounds. Distinct interactions with postranslationally modified cysteines present in the active site of the enzyme were observed. Modeling shows that water molecule activated by a metal ion may easily directly attack the docked acrylonitrile to transform this molecule into acryloamide. Thus docking studies provide support for one of the reaction mechanisms discussed in the literature. Figure Crystalographic structure of Pseudonocardia thermophila JCM 3095 nitrile hydratase (a) and the non-standard active site (b)     

Enantioselective hydrolysis of O-acetylmandelonitrile to O-acetylmandelic acid by bacterial nitrilases

Bacteria were enriched from soil samples, using benzylcyanide, -methyl-, -ethyl- or -methoxybenzyl-cyanide as the sole source of nitrogen. All isolated strains belonged to the genus Pseudomonas. Resting cells of the isolates hydrolysed O-acetylmandelonitrile to O-acetylmandelic acid, O-acetylmandelic acid amide and mandelic acid. From racemic O-acetylmandelonitrile all isolates preferentially formed R(–)-acetylmandelic acid ( = d-acetylmandelic acid). The enantioselective hydrolysis of O-acetylmandelonitrile could also be demonstrated in vitro. Crude extracts did not hydrolyse O-acetylmandelic acid amide indicating an enantioselective nitrilase rather than a nitrile hydratase/amidase system.     

Isolation and Characterization of a Nitrile-Hydrolysing Bacterium Isoptericola variabilis RGT01

A nitrile-hydrolysing bacterium, identified as Isoptericola variabilis RGT01, was isolated from industrial effluent through enrichment culture technique using acrylonitrile as the carbon source. Whole cells of this microorganism exhibited a broad range of nitrile-hydrolysing activity as they hydrolysed five aliphatic nitriles (acetonitrile, acrylonitrile, propionitrile, butyronitrile and valeronitrile), two aromatic nitriles (benzonitrile and m-Tolunitrile) and two arylacetonitriles (4-Methoxyphenyl acetonitrile and phenoxyacetonitrile). The nitrile-hydrolysing activity was inducible in nature and acetonitrile proved to be the most efficient inducer. Minimal salt medium supplemented with 50 mM acetonitrile, an incubation temperature of 30 °C with 2 % v/v inoculum, at 200 rpm and incubation of 48 h were found to be the optimal conditions for maximum production (2.64 ± 0.12 U/mg) of nitrile-hydrolysing activity. This activity was stable at 30 °C as it retained around 86 % activity after 4 h at this temperature, but was thermolabile with a half-life of 120 min and 45 min at 40 °C and 50 °C respectively.     

Inhibitors of dipeptidyl peptidase 8 and dipeptidyl peptidase 9. Part 1: identification of dipeptide derived leads

Dipeptide derivatives bearing various P2 residues and pyrrolidine derivatives as P1 mimics were evaluated in order to identify lead structures for the development of DPP8 and DPP9 inhibitors. Structure–activity-relationship data obtained in this way led to the preparation of a series of α-aminoacyl ((2S, 4S)-4-azido-2-cyanopyrrolidines). These compounds were shown to be nanomolar DPP8/9 inhibitors with modest overall selectivity toward DPP IV and DPP II.