Formation Of Isothiocyanates Research Articles

Covalent cross-linking of proteins by carbon disulfide.

Carbon disulfide is known to react with amino groups of proteins to generate dithiocarbamates (2). We observed covalent cross-linking of dithiocarbamate-derivatized proteins under physiological conditions which may occur through several mechanisms. Evidence for the structure of these covalent bridges and the reactive intermediate was obtained using 13C NMR spectroscopy in conjunction with specific isotopic labeling. On incubation at 37 degrees C oxidative coupling of dithiocarbamates generated bis(thiocarbamoyl) disulfides (3) which were reduced by cysteine. In addition, an electrophilic isothiocyanate (4) was generated from decomposition of the dithiocarbamate. Nucleophilic addition of sulfhydryl and amine moieties to the isothiocyanate produced dithiocarbamate ester (5) and thiourea linkages (6), respectively. Evidence for the presence of inter- and intramolecular cross-links was obtained using denaturing polyacrylamide gel electrophoresis under reducing conditions. The formation of isothiocyanate in neutral solution, through elimination of sulfhydryl ion, was correlated with increased pKa values of the parent amine of amino acids. Dithiocarbamates derived from terminal amino groups of proteins did not appear to generate isothiocyanate or form thiourea or dithiocarbamate ester. Both the thiourea and the dithiocarbamate ester were stable at reduced pH, whereas in alkaline media the thiourea was stable but dithiocarbamate ester was hydrolyzed. Although the disulfide and ester linkages were formed more rapidly than the thiourea, generation of the latter appeared to be irreversible, leading to its gradual accumulation over a longer period of time. Generation of isothiocyanate by CS2-derived dithiocarbamates and subsequent covalent cross-linking of proteins may provide a molecular mechanism for CS2-induced axonopathy.

The watercress glucosinolate-myrosinase system: a feeding deterrent to caddisflies, snails and amphipods.

Watercress (Nasturtium officinale) possesses the glucosinolate-myrosinase system. This system is regarded as a classic example of chemical defense for terrestrial crucifers. Damage of watercress initiates myrosinase-mediated hydrolysis of phenylethyl glucosinolate to a toxic endproduct, phenylethyl isothiocyanate. In multiple choice tests, the amphipod Gammarus pseudolimnaeus, the limnephilid caddisflies Hesperophylax designatus and Limnephilus sp., and the physid snail Physella sp. all strongly preferred (10X) yellowed senescent watercress (FY) over fresh green watercress (FG), despite the 2X higher nitrogen content of green watercress (6.9% for FG vs 3.8% for FY). Green watercress contained 10-40 X more glucosinolate than FY watercress (6.4-8.5 mg/g wet for FG vs 0.2-0.7 mg/g wet for FY). However, when the watercress was heated (ca 70°C), to deactivate the myrosinase enzyme, multiple choice tests showed that these species shift their preferences to heated green watercress (HG). Heating deactivated the deterrent effect and overall preference (consumption) was HG ≥ HY > FY ≫ FG for Gammarus. HG > HY ≥ FY ≫ FG for Hesperophylax, HG > FY ≥HY ≥ FG for Limnephilus, and HG ≥ FY > HY ≥ FG for Physella. Thus heating resulted in a shift in preference from the low glucosinolate, but low nitrogen, unheated yellowed tissue to the high nitrogen green tissue. These results suggest that deactivation of the myrosinase enzyme, and hence isothiocyanate production, results in a shift in preference. Preliminary results with Hesperophylax indicate that addition of myrosinase to the test water, which resulted in the formation of isothiocyanate, results in a significant decrease in HG consumption from control levels (p < 0.001) and no change in preference for HY watercress. With Gammarus, myrosinase resulted in reduced consumption of both green and yellowed watercress, but no significant differential effect. These results provide evidence that the glucosinolate-myrosinase system, recognized as the principle deterrent system of terrestrial crucifers, is the feeding deterrent in watercress and also suggest that in the absence of a functioning deterrent system, nitrogen content may influence consumption.

Unexpected Course of Thiocyanation of 1,6‐Methano[10]annulene. Elimination of Thiocyanogen from a Diisothiocyanate

AbstractThe isolation of the syn,syn‐adduct 5 in the reaction of 1,6‐methano[10]annulene (1) with the bulky pseudo‐halogen (SCN)2 indicates a preferred exo attack of electrophiles on 1, in spite of a possible steric interference with the methylene bridge. The formation of the unexpected isothiocyanates 4 and 5 is explained in terms of an addition‐isomerization‐elimination sequence. The novel elimination of (SCN)2 from a diisothiocyanate is investigated.

A magnetic super lattice

Glucosinolates are a group of secondary plant metabolites that are found in the Brassicaceae family. Upon hydrolysis by the endogenous enzyme myrosinase, a large number of compounds can be formed of which some are potentially anticarcinogenic, while others are largely inactive. Furthermore, some bioactive compounds are unstable. Therefore, it is not only important to determine the type and amount of glucosinolates present or hydrolysed in a given plant, but it is also relevant to investigate the type of hydrolysis products. In this research, the effect of combined pressure–temperature treatments (100–500 MPa, 20–40 °C) on the glucosinolate conversion and the kind of hydrolysis products was studied in broccoli, both during treatment and after autolysis. The results, showed that high pressure can induce glucosinolate hydrolysis during treatment, promote the formation of isothiocyanates after treatment and that relatively more indole oligomers are formed during treatment than during autolysis. These results indicate that pressure treatment limits the loss of glucosinolates and its health beneficial products.

Effects of pH and Ferrous Ion on the Degradation of Glucosinolates by Myrosinase

During the enzymatic degradation of sinigrin, the release of glucose and the formation of allyl isothiocyanate via subsequent cleavage of the aglucon were studied in the presence or absence of ferrous ion over a pH range of 3.5 ~ 7.5. The liberation of glucose increased linearly with the time of enzymatic cleavage of sinigrin for the first 20 min at the pHs used, and no inhibition of glucose liberation was caused by ferrous ion at the concentration tried.On the other hand, the effects of ferrous ion on the formation of isothiocyanate changed greatly with changes of pH of the reaction medium. At pH 4.5 and 5.5, formation of isothiocyanate was strongly inhibited by ferrous ion, while such an effect of ferrous ion was notably depressed at pH 6.5 and disappeared at pH 7.5. These results were also confirmed by gas chromatographic analysis of the volatile cleavage products of the glucosinolates prepared from the seed meal of hakuran (an artificial variety of Brassica napus). From these results, it was suggested...

Effects of thiol compounds on the formation of nitriles from glucosinolates.

The effects of L-cysteine, reduced glutathione, dithiothreitol, cysteamine, thiobenzoate, thiomalate, and thiophenol on the enzymatic degradation of sinigrin were investigated in combination with ferrous ion at different pHs (5.0-7.5). Formation of allyl isothiocyanate was greatly inhibited by addition of both the thiol compounds and ferrous ion to the reaction medium at pH 5.0 or 6.5. Combined effects of the thiol compounds and ferrous ion on the formation of volatile products was also studied by gas chromatography using a mixture of allyl, 3-butenyl, and 4-pentenyl glucosinolates (1:4:1) as substrate. It was confirmed that the greater part of the volatile components produced in the presence of both the thiol compounds and ferrous ion was allyl, 3-butenyl, and 4-pentenyl cyanides and their corresponding cyanoepithioalkanes, even though the reaction medium was adjusted to pH 6.5. Similar results were obtained when silver sinigrate, an analogous model compound to the aglucon of sinigrin, was degraded by the addition of sodium chloride in the presence of both the thiol compounds and ferrous ion. The results suggest that in combination with ferrous ion, such common thiol compounds as L-cysteine and glutathione may be concerned in the production of nitriles from glucosinolates in natural systems, and that the acceleration of nitrile formation is probably attributed to much more rapid desulfuration than the progress of Lessen rearrangement of aglucon.

The Reaction of Olefins with a Mixture of Iodine and Mercury(II) Thiocyanate. Predominant Formation of vic-Iodo(isothiocyanato)alkanes

Abstract Treatment of olefins with a mixture of iodine and mercury(II) thiocyanate in benzene or diethyl ether gives vic-iodo(isothiocyanato)alkanes and vic-iodo(thiocyanato)alkanes in a high yield, the former being predominant. Similar results were obtained by using silver(I) and thallium(I) thiocyanates, though both the yield and the selectivity are slightly lower. By use of potassium thiocyanate and copper(I) isothiocyanate in place of mercury(II) thiocyanate, β-iodo thiocyanates were mainly formed. A reaction scheme involving initial formation of an iodonium ion from olefin and ISCN (formed in situ) and a subsequent attack of complex anion I(SCN)2− has been proposed to account for this predominant formation of β-iodo isothiocyanates.

Effects of metal ions on benzylglucosinolate degradation in Lepidium sativum seed autolysates

The effects of varying concentrations of Fe 2+ (5 × 10 −5 −5 × 10 −1 M) on benzylglucosinolate degradation in Lepidium sativum seed autolysates were investigated. Increased glucosinolate decomposition was observed over the whole range with a maximum effect at ca 6 × 10 −3 M Fe 2+, at which point glucosinolate degradation was more than three times that obtained in the absence of added Fe 2+ . Nitrile formation was especially enhanced in the presence of all concentrations of Fe 2+ studied, and maximum amounts were obtained at ca 6 × 10 −3 M Fe 2+ when a more than four-fold increase over quantities produced in the absence of Fe 2+ was observed. Thiocyanate formation was also promoted with a maximum at ca 4 × 10 −3 M Fe 2+, but isothiocyanate production was considerably reduced in allcases. It is suggested that Fe 2+ inhibits isothiocyanate formation by interfering with the availability of ascorbic acid which is a proven co-factor for most thioglucosidase isoenzymes, but that an Fe 2+-ascorbate complex might then be responsible for promoting enzymic production of nitrile. The effects of a limited range of concentrations of Fe 3+ and Cu + were also studied, and results related to those for Fe 2+. The relevance of the findings to natural systems and to glucosinolate-containing foods is briefly discussed.

Effects of pH and ascorbate on benzylglucosinolate degradation in seed extracts of Lepidium sativum

The effects of pH on the enzymic degradation of benzylglucosinolate in Lepidium sativum seed autolysates were investigated both with and without addition of the enzyme co-factor ascorbic acid. Benzyl cyanide, isothiocyanate, thiocyanate and alcohol were identified in autolysates, although only traces of the alcohol were obtained. The nitrile was always the major product (80% of total glucosinolate products) even at pH 8 and 9 when the usually accepted, proton-dependent mechanism of nitrile production cannot be operative. Thiocyanate was always the second most abundant product. In the absence of added ascorbate, isothiocyanate production decreased with increasing pH, again contrary to accepted theory. L. sativum seeds thus constitute an inherently nitrile-producing system which exhibits ‘anomalous’ glucosinolate degradation. In the absence of added ascorbate, thiocyanate was the only product which was formed in approximately constant amounts, whatever the pH, so its mechanism of production is not necessarily pH-dependent. The presence of added ascorbate in general promoted enzyme activity and showed a maximum effect at ca pH 5, although minimum isothiocyanate formation was observed at that pH. At pH 4 and below, there was less glucosinolate degradation in the presence of added ascorbate than in its absence, and the conclusion is reached that at relatively high acidities the enzyme co-factor behaves as an inhibitor.

Gas chromatographic and mass spectrometric properties of ethyl esters of dithiocarbamic acids of primary and secondary amines

A method has been devised for determining primary and secondary amines in the form of dithiocarbamic acid ethyl esters by high-resolution gas chromatography and mass spectrometry. The dithiocarbamic acid ethyl ester derivatives of primary amines decompose by pyrolysis in the injection port of a chromatograph to isothiocyanates, whereas derivatives of secondary amines do not decompose. The mechanism of isothiocyanate formation from dithiocarbamic acid esters was established by identifying the pyrolysis products. This method permits simultaneous differentiation and determination of primary and secondary amines.

Effects of a Lepidium sativum enzyme preparation on the degradation of glucosinolates

The effects of a crude enzyme extract prepared from Lepidium sativum seeds, on the degradation of three pure glucosinolates (allyl-, benzyl- and 2-phenethyl-) were investigated in the presence of the known enzyme co-factor, ascorbic acid. Isothiocyanates and nitriles were obtained but no thiocyanates. For maximum isothiocyanate formation there was an optimum concentration of ascorbic acid which varied directly with the concentration of substrate but was independent of the particular glucosinolate. Formation of isothiocyanate from any glucosinolate was linear with time but enzymic production of 2-phenethyl isothiocyanate was activated by ascorbic acid to a greater extent than for the other two glucosinolates studied. Isothiocyanate was still the major product even at low pH although the thioglucosidase was only weakly active. Nitrile formation was always erratic in the presence of ascorbic acid. In the absence of ascorbic acid thioglucosidase was still active although to a much lesser extent, but in these circumstances benzyl thiocyanate was an additional product. There is thus a thiocyanate-forming factor in the extract of L. sativum seeds which is inactivated in the presence of ascorbic acid. This factor did not cause the formation of thiocyanate from 2-phenethylglucosinolate.

The Preparation of Vinylenedi-Isothiocyanate

Abstract The preparation and some properties of vinylene dithiocyanate were described by Soderback1 in 1925 and, more recently, in 1969 some substituted thiocyanato-isothiocyanato ethylenes by Zbiral and Hengstberger2. We have reported on the formation of isothiocyanates by the fission of N-heterocyclic compounds in the presence of thiophosgene and base3. This paper describes a further application of this method to the preparation of vinylenedi-isothiocyanate (1) from imidazole.

The interaction of organic isothiocyanates with complexes of ruthenium and rhodium. Formation of Π-bound isothiocyanate, isonitrile-dithiocarbonimidato complexes and a new route to isonitrile-dioxygen complexes of rhodium.

Simple π-bound isothiocyanate complexes result from the interaction of Ru(CO) 2(PPh 3) 3 with RNCS (R  Ph, Et, Me). Both RU(CO) 2(PPh 3) 2(π-RNCS) (I) and Ru(Co) 2(PPh 3) 3 react with excess RNCS to yield the isonitrile-dithiocarbonimidato derivatives, Ru(CO) (CNR) (S 2CNR) (PPH 3) 2(II). When RhCl(PPh 3) 3 reacts with RNCS (R  Bz, c -hex, Ph, tBu, nBu, Et), a simple π-RNCS adduct may not be isolated but is a presumed intermediate in the formation of the isonitrile-dithiocarbonimidato derivatives RhCl(CNR) (S 2CNR) (PPh 3) 2(III). Methyl iodide effects alkylation at the nitrogen of the dithiocarbonimidato ligand of III to give the series of cationic complexes, [RhCl (CNR) {S 2CN(Me)R} PPh 3) 2]I (R  Bz, Ph, Et) (IV). Complex III also reacts with triphenylphosphine to give in solution trans -RhCl(CNR) (PPh 3) 2, which rapidly coordinates dioxygen to give complexes of the type. RhCl(CNR) (PPh 3) 2(O 2) (R  Ph, c -hex. tBU, nBu) (V).

The Thallium(I) Salt-catalyzed Formation of Isothiocyanates from Isocyanides and Disulfides

Abstract The reactions of various isocyanides with diacyl disulfides or tetraethylthiuram disulfide occur smoothly in the presence of thallium(I) acetate and thiocarboxylates in various organic solvents to give the corresponding isothiocyanates in good yields. Lead(II) acetate has an activity almost identical with that of thallium(I), while cadmium(II) and silver(I) acetates and copper(I) oxide show a slightly lower activity than the above thallium and lead salts. An ionic scheme involving a complex formation between the metal salt and one S atom of the disulfide, followed by a nucleophilic attack of isocyanide on the adjacent S atom, is proposed for this reaction. It is revealed that the reaction of isocyanide with one equivalent of thallium(III) thiobenzoate in refluxing chloroform similarly affords a good yield of the isothiocyanate through the above mechanism after the decomposition of the thallium(III) salt to thallium(I) thiobenzoate and dibenzoyl disulfide, rather than through a pathway involving thiothallation (α-addition).

Sulfur‐containing polymers. XVIII. Preparation and properties of thiuram polysulfide polymers

AbstractThiuram polysulfide polymers have been prepared from alkali metal bisdithiocarbamates either by oxidation with ammonium persulfate or by polycondensation with sulfur chlorides. In some cases, isothiocyanate formation and/or thiourea formation were noticed. The polymer properties were significantly affected by the diamines used. Polymers derived from p‐phenylenediamine decomposed gradually at room temperature with the liberation of elemental sulfur. Polymers based on aliphatic primary diamines were more stable. Piperazine gave the most stable polymer.

Kinetics and mechanism of hydrolysis of O-aryl N-phenylthiocarbamates

In kinetic studies of the hydrolysis ofaseries of O-aryl N-phenylthiocarbamates, evidence for the formation of phenyl isothiocyanate is a decisive argument for an E1cB mechanism. The high value of the Hammett parameter (ρ 3.0) and the positive value of the entropy of activation (ΔS‡+ 10.8 cal mol–1 K–1) are discussed as mechanistic criteria which can be used to establish the occurrence of an EIcB mechanism when the intermediate cannot be isolated.

Formation of phenyl thiocyanate and phenyl isothiocyanate in the reaction of benzenediazonium sulfate, cupric ion and thiocyanate ion (author's transl)

In the Sandmeyer reaction of benzenediamnium ion with thiocyanate ion in the presence of cupric ion, the yield of phenyl thiocyanate (I) increased up to 30% with the increase in the molar ratio of thiocyanate ion to cupric ion, in the pH range of 8.0-8.5, whereas that of phenyl iso-thiocyanate (II) increased up to 40% with the decrease of the molar ratio of these reactsnts in the pH range of 1.0-1.5. For the explanation of the difference in the yield of these products, relationship between the reaction of Cu2+ to SCN- and the results of Sandmeyer reaction was examined. The amount of cuprous thiocyanate prpduced and the concentration of cupric thiocyanate in the solution were proportional to the yields of I and II, respectively. Accordingly, cuprous thiocyanate and cupric thiocyanate are considered to be responsible for the formation of I and II, respectively.

Reaction of 4,4′-dimethoxydiphenylmethanimine with carbon disulfide

The reaction of 4,4′-dimethoxydiphenylmethanimine with carbon disulfide in bromoform was studied at temperatures of 40°, 50°, and 60° in sealed tubes. The products from this reaction are 4,4′-dimethoxythiobenzophenone and 4,4′-dimethoxydiphenylmethaniminium thiocyanate. The proposed mechanism postulates primary attack on the carbon atom of carbon disulfide by the imine nitrogen leading to a resonance stabilized intermediate followed by ring closure with formation of a 4-membered ring, ▪ which is unstable and decomposes to form thioketone and isothoicyanic acid. Supporting evidence for the proposed mechanism was drawn from kinetic studies, NMR studies, the effect of copper on the reaction system and the reaction of the benzyl substituted imine N-benzyl-4,4′-dimethoxydiphenylmethanimine (Schonberg's Reagent) with carbon disulfide at 43°. The formation of benzyl isothiocyanate in the system was inferred from the presence of N,N-dibenzylthiourea. The presence of benzyl isothiocyanate in the substituted imine—CS 2 system suggests that the initial decomposition product from the four membered ring intermediate in the imine—CS 2 system is HNCS. The work suggests that dithiocarbamic acids in oxidizing metallic copper may not react through a dithiocarboxyl group in a classical sense but through a zwitterionic form of the molecule where the hydrogen is attached to the nitrogen stom.