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Isothiocyanate

From Wikipedia, the free encyclopedia

General structure of an isothiocyanate.
General structure of an isothiocyanate.

Isothiocyanate is the chemical group –N=C=S, formed by substituting the oxygen in the isocyanate group with a sulfur. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. These natural isothiocyanates, such as allyl isothiocyanate, are also known as mustard oils. An artificial isothiocyanate, phenyl isothiocyanate, is used for amino acid sequencing in the Edman degradation.

YouTube Encyclopedic

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  • The Truth About Wasabi - Speaking of Chemistry
  • Jed Fahey, Sc.D. on Isothiocyanates, the Nrf2 Pathway, Moringa & Sulforaphane Supplementation
  • The science of spiciness - Rose Eveleth
  • Edman Degradation
  • Allyl isothiocyanate Meaning

Transcription

If you’ve ever eaten at a sushi restaurant then you’ve probably tasted that green spicy paste people like to call wasabi. truth is, you’ve probably never tried real wasabi. [Intro] You slip a sushi roll into your mouth. Beneath the raw fish, rice and seaweed flavors you detect the hint of something spicy, like horseradish, rising up into your nose. Suddenly your sinuses are the clearest they’ve ever been in your life, and a prickling rush of heat moves up your neck, into your head, which starts thudding--possibly pleasantly. You overdid it with the wasabi. Only, it’s probably not wasabi. That is, unless you’re actually in Japan, or imported the valuable plant at a hefty price, or found one of the few growers outside Japan. The wasabi most of us have eaten is most likely a mix of European horseradish, hot mustard and green dye to give it the pistachio-colored hue of the Real McCoy. Even in Japan, only a minority of restaurants serve real thing. That’s because true Japanese wasabi is extremely tricky to cultivate. Wasabi likes to be lovingly enveloped by a steady stream of water, reminiscent of rocky Japanese mountain stream beds where the plant grows endemically. And wasabi is not a fan of crowds. When planted en masse in a greenhouse, the plant can easily succumb to infectious disease. Wasabi’s diva-like persuasion makes it a finicky crop, but also an extremely lucrative one. Case in point: Here in Berlin, you can import a 100 gram wasabi stem for 45 Euros, about 50 dollars. And listen—if you’re going to fork out this kind of cash for some wasabi, don’t embarrass yourself and call it a root—it’s called a rhizome. In fact the part of the wasabi plant that gets grated or pulverized into a paste is the above-ground stem component of the rhizome. You can see here where the leaves have either fallen or been cut off. But how does this wasabi compare to its common substitute horseradish? Both get their spicy zing from a family of compounds called isothiocyanates—although wasabi typically contains more of the spicy chemicals than horseradish. These isothiocyanates are kept on a chemical leash—they are attached to sugar molecules. When wasabi cells are pulverized during grating, they release enzymes that split apart the spice from the sugar, giving wasabi a zing with a hint of sweetness. The dominant flavor—what foodies would call the top note--in both comes from a chemical called allyl isothiocyanate. The main flavor differences in wasabi and horseradish come from different relative proportions of other isothiocyanates. For example, wasabi has more 6-Methylsulfinylhexyl isothiocyanate, a-k-a 6-MITC, for obvious reasons. Foodies aren’t the only folks interested in wasabi’s spicy chemicals. Medical researchers have their eye on 6-MITC, which some claim can alleviate symptoms in a wide variety of disorders including asthma, cancer, and neurodegenerative diseases. But for anyone with an appetite for pleasurable pain: try real wasabi. Find a restaurant that starts grating the wasabi only after you’ve placed your order, or lets you grate your own wasabi, ideally with a traditional shark skin tool called oroshigane. That’s the only way you’ll get the full kick. Wasabi flavors start floating away as soon as they’re released. Within about 15 minutes, the taste apoca lypse you were hoping for is barely a spicy boot to the head. And if you’re a glutton for spice, be sure to check out the description for the articles that inspired this episode and this video on sriracha from our friends at ACS Reactions. Thanks for watching and feel free to subscribe and share.

Contents

Synthesis and reactions

The general method for the formation of isothiocyanates proceeds through the reaction between a primary amine (e.g. aniline) and carbon disulfide in aqueous ammonia. This results in precipitation of the ammonium dithiocarbamate salt, which is then treated with lead nitrate to yield the corresponding isothiocyanate.[1] Another method relies on a tosyl chloride mediated decomposition of dithiocarbamate salts that are generated in the first step above.[2]

Isothiocyanates may also be accessed via the thermally-induced fragmentation reactions of 1,4,2-oxathiazoles.[3] This synthetic methodology has been applied to a polymer-supported synthesis of isothiocyanates.[4]

Isothiocyanates are weak electrophiles. Akin to the reactions of carbon dioxide, nucleophiles attack at carbon.

Reflecting their electrophilic character, isothiocyanates are susceptible to hydrolysis.

Biological activity

Isothiocyanates occur widely in nature and are of interest in food science and medicine. Vegetable foods with characteristic flavors due to isothiocyanates include wasabi, horseradish, mustard, radish, Brussels sprouts, watercress, papaya seeds, nasturtiums, and capers. These species generate isothiocyanates in different proportions, and so have different, but recognisably related, flavors. They are all members of the order Brassicales, which is characterised by the production of glucosinolates, and of the enzyme myrosinase, which acts on glucosinolates to release isothiocyanates.

Phenethyl isothiocyanate (PEITC) and sulforaphane inhibit carcinogenesis and tumorigenesis in certain circumstances. Their mechanism of action is proposed to involve inhibition of cytochrome P450 enzymes, which oxidize compounds such as benzo[a]pyrene and other polycyclic aromatic hydrocarbons (PAHs) into more polar epoxy-diols, which can then cause mutation and induce cancer development.[6] Phenethyl isothiocyanate (PEITC) has been shown to induce apoptosis in certain cancer cell lines, and, in some cases, is even able to induce apoptosis in cells that are resistant to some currently used chemotherapeutic drugs, for example, in drug-resistant leukemia cells that produce the powerful apoptosis inhibitor protein Bcl-2.[7] Furthermore, isothiocyanates have been the basis of a drug in development that replaces the sulfur bonds with selenium, with far stronger potency against melanoma.[8] Certain isothiocyanates have also been shown to bind to the mutated p53 proteins found in many types of tumors, causing an increase in the rate of cell death.[9][10]

The results on the genotoxic effects of the isothiocyanates and glucosinolate precursors are conflicting.[11] Some authors report weak genotoxicity for allyl isothiocyanate and phenethyl isothiocyanate.[citation needed] Induction of point mutations in Salmonella TA98 and TA100, repairable DNA damage in E.coli K-12 cells, and clastogenic effects in mammalian cells by extracts from cruciferous vegetables have also been observed.[citation needed] The goitrogenic effect of Brassicaceae (to which Cruciferous belong) vegetables, interfering with iodine uptake, is also a concern at elevated doses.[12] The average intake of such sulfur-containing compounds through supplementation should not exceed normal levels of consumption.[citation needed]

The transcription factor Nrf2 is required for isothiocyanate pharmacologic activity.[13]

Coordination chemistry

Isothiocyanate and its linkage isomer thiocyanate are ligands in coordination chemistry. Thiocyanate is more common ligand.

Structure of Pd(Me2N(CH2)3PPh2)(SCN)(NCS).[14]
Structure of Pd(Me2N(CH2)3PPh2)(SCN)(NCS).[14]

See also

References

  1. ^ Dains FB; Brewster RQ; Olander CP (1926). "Phenyl Isothiocyanate". Organic Syntheses. 6: 72.; Collective Volume, 1, p. 447
  2. ^ Wong, R; Dolman, SJ (2007). "Isothiocyanates from tosyl chloride mediated decomposition of in situ generated dithiocarbamic acid salts". The Journal of Organic Chemistry. 72 (10): 3969–3971. doi:10.1021/jo070246n. PMID 17444687.
  3. ^ O’Reilly, RJ; Radom, L (2009). "Ab initio investigation of the fragmentation of 5,5-diamino-substituted 1,4,2-oxathiazoles". Organic Letters. 11 (6): 1325–1328. doi:10.1021/ol900109b. PMID 19245242.
  4. ^ Burkett, BA; Kane-Barber, JM; O’Reilly, RJ; Shi, L (2007). "Polymer-supported thiobenzophenone : a self-indicating traceless 'catch and release' linker for the synthesis of isothiocyanates". Tetrahedron Letters. 48 (31): 5355–5358. doi:10.1016/j.tetlet.2007.06.025.
  5. ^ Ortega-Alfaro, M. C.; López-Cortés, J. G.; Sánchez, H. R.; Toscano, R. A.; Carrillo, G. P.; Álvarez-Toledano, C. (2005). "Improved approaches in the synthesis of new 2-(1, 3-thiazolidin-2Z-ylidene)acetophenones". Arkivoc. 2005 (6): 356–365. doi:10.3998/ark.5550190.0006.631.
  6. ^ Zhang, Y; Kensler, TW; Cho, CG; Posner, GH; Talalay, P (1994). "Anticarcinogenic activities of sulforaphane and structurally related synthetic norbornyl isothiocyanates". Proceedings of the National Academy of Sciences of the United States of America. 91 (8): 3147–3150. Bibcode:1994PNAS...91.3147Z. doi:10.1073/pnas.91.8.3147. PMC 43532. PMID 8159717.
  7. ^ Tsimberidou AM, Keating MJ (Jul 1, 2009). "Treatment of fludarabine-refractory chronic lymphocytic leukemia". Cancer. 115 (13): 2824–36. doi:10.1002/cncr.24329. PMID 19402170.
  8. ^ Madhunapantula SV, Robertson GP (Mar 23, 2011). "Therapeutic Implications of Targeting AKT Signaling in Melanoma". Enzyme Res. 2011: 327923. doi:10.4061/2011/327923. PMC 3065045. PMID 21461351. Lay summary.
  9. ^ Wang X, Di Pasqua AJ, Govind S, McCracken E, Hong C, Mi L, Mao Y, Wu JY, Tomita Y, Woodrick JC, Fine RL, Chung FL (Jan 11, 2011). "Selective depletion of mutant p53 by cancer chemopreventive isothiocyanates and their structure-activity relationships". J Med Chem. 54: 809–816. doi:10.1021/jm101199t. PMC 3139710. PMID 21241062. (primary source)
  10. ^ Wall, Tim (March 10, 2011). "How broccoli fights cancer". Discovery News.
  11. ^ Higdon JV, Delage B, Williams DE, Dashwood RH (March 2007). "Cruciferous vegetables and human cancer risk: epidemiologic evidence and mechanistic basis". Pharmacol Res. 55 (3): 224–36. doi:10.1016/j.phrs.2007.01.009. PMC 2737735. PMID 17317210.
  12. ^ Truong, Thérèse; Baron-Dubourdieu, Dominique; Rougier, Yannick; Guénel, Pascal (August 2010). "Role of dietary iodine and cruciferous vegetables in thyroid cancer: a countrywide case-control study in New Caledonia". Cancer Causes & Control. 21 (8): 1183–1192. doi:10.1007/s10552-010-9545-2. ISSN 0957-5243. PMC 3496161. PMID 20361352.
  13. ^ McWalter, Gail K.; Higgins, Larry G.; McLellan, Lesley I.; Henderson, Colin J.; Song, Lijiang; Thornalley, Paul J.; Itoh, Ken; Yamamoto, Masayuki; Hayes, John D. (1 December 2004). "Transcription Factor Nrf2 Is Essential for Induction of NAD(P)H:Quinone Oxidoreductase 1, Glutathione S-Transferases, and Glutamate Cysteine Ligase by Broccoli Seeds and Isothiocyanates". The Journal of Nutrition. 134 (12): 3499S–3506S. doi:10.1093/jn/134.12.3499S. Retrieved 8 April 2018 – via jn.nutrition.org.
  14. ^ Gus J. Palenik, George Raymond Clark "Crystal and Molecular Structure of Isothiocyanatothiocyanato-(1-diphenylphosphino-3-dimethylaminopropane)palladium(II)" Inorganic Chemistry, 1970, volume 9, pp 2754–2760. doi:10.1021/ic50094a028

External links


This page was last edited on 10 November 2018, at 00:03
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