“…Three chemical reactions of HOSCN and (SCN) 2 , the major species produced from thiocyanate by HRP, , readily rationalize the observed products. All three reactions are initiated by electrophilic addition of a thiocyanate moiety to a vinyl group, a well-precedented reaction of HOSCN and (SCN) 2 that generates a carbocationic intermediate. , The electrophilic addition is then followed by one of three termination processes: (a) trapping of the resulting carbocation by a thiocyanate anion (Scheme , reaction a ), (b) trapping of the carbocation by a water molecule (Scheme , reaction b ), or (c) loss of a proton to regenerate a double bond (Scheme , reaction c ). 1 Potential Reactions of Hypothiocyanous Acid with a Heme Vinyl Group…”
The mammalian peroxidases eosinophil peroxidase, lactoperoxidase (LPO), and myeloperoxidase oxidize thiocyanate to the antimicrobial agents hypothiocyanous acid (HOSCN) and (SCN)2 and are part of a defense system that protects the host from infections. Horseradish peroxidase (HRP), a plant enzyme, also oxidizes thiocyanate. We report here that the prosthetic heme vinyl groups of HRP react with the catalytically generated HOSCN and (SCN)2 to form at least nine vinyl-modified heme adducts. Mass spectrometry combined with analysis of the equivalent reactions of HRP reconstituted with 2- or 4-cyclopropylheme, or mesoheme-d4, shows that all of the prosthetic heme modifications result from addition of oxidized thiocyanate to the heme vinyl groups. No delta-meso-substitution of the heme was observed, in contrast to what is observed with radical agents. Model studies show that incubation of either HRP with preformed HOSCN or a solution of heme with preformed (SCN)2 gives rise to the same products obtained in the HRP-catalyzed reaction. Model studies also demonstrate that the SCN* radical, if formed, should add to a meso-carbon. These findings implicate an electrophilic addition mechanism. In contrast, oxidation by LPO of thiocyanate, the normal substrate of this enzyme, does not result in heme modification. In view of the demonstrated intrinsic reactivity of the heme group, LPO must actively suppress heme modification. As the key difference between LPO (and other mammalian peroxidases) and HRP is the presence of two covalent ester links between the heme and the protein, we propose that these links contribute to steric protection of the adjacent heme vinyl groups.
“…Three chemical reactions of HOSCN and (SCN) 2 , the major species produced from thiocyanate by HRP, , readily rationalize the observed products. All three reactions are initiated by electrophilic addition of a thiocyanate moiety to a vinyl group, a well-precedented reaction of HOSCN and (SCN) 2 that generates a carbocationic intermediate. , The electrophilic addition is then followed by one of three termination processes: (a) trapping of the resulting carbocation by a thiocyanate anion (Scheme , reaction a ), (b) trapping of the carbocation by a water molecule (Scheme , reaction b ), or (c) loss of a proton to regenerate a double bond (Scheme , reaction c ). 1 Potential Reactions of Hypothiocyanous Acid with a Heme Vinyl Group…”
The mammalian peroxidases eosinophil peroxidase, lactoperoxidase (LPO), and myeloperoxidase oxidize thiocyanate to the antimicrobial agents hypothiocyanous acid (HOSCN) and (SCN)2 and are part of a defense system that protects the host from infections. Horseradish peroxidase (HRP), a plant enzyme, also oxidizes thiocyanate. We report here that the prosthetic heme vinyl groups of HRP react with the catalytically generated HOSCN and (SCN)2 to form at least nine vinyl-modified heme adducts. Mass spectrometry combined with analysis of the equivalent reactions of HRP reconstituted with 2- or 4-cyclopropylheme, or mesoheme-d4, shows that all of the prosthetic heme modifications result from addition of oxidized thiocyanate to the heme vinyl groups. No delta-meso-substitution of the heme was observed, in contrast to what is observed with radical agents. Model studies show that incubation of either HRP with preformed HOSCN or a solution of heme with preformed (SCN)2 gives rise to the same products obtained in the HRP-catalyzed reaction. Model studies also demonstrate that the SCN* radical, if formed, should add to a meso-carbon. These findings implicate an electrophilic addition mechanism. In contrast, oxidation by LPO of thiocyanate, the normal substrate of this enzyme, does not result in heme modification. In view of the demonstrated intrinsic reactivity of the heme group, LPO must actively suppress heme modification. As the key difference between LPO (and other mammalian peroxidases) and HRP is the presence of two covalent ester links between the heme and the protein, we propose that these links contribute to steric protection of the adjacent heme vinyl groups.
“…Since the emergence of the thiocyanogen chloride as an electrophilic thiocyanating reagent in 1958, several major contributions were reported in the last half of the century. In this section, the synthesis of this SCN source and a selection of its applications will be described [8] …”
Section: Historical Contextmentioning
confidence: 99%
“…Since the emergence of the thiocyanogen chloride as an electrophilict hiocyanating reagent in 1958, severalm ajor contributions were reported in the last half of the century.I nt his section, the synthesis of this SCN source and as election of its applications will be described. [8] In 1958, Bacon and Angusr eported the use of the thiocyanogen chloride I as an electrophilict hiocyanogen reagent (Scheme 1). [9] It was prepared from thiocyanogen 1 and gaseous chlorine and kept in solution as it is stable in solvents such as toluene, CHCl 3 ,a nd CCl 4 .N ote that as it decomposed rapidly over time, it was generally used in as hort time after being made.…”
Organothiocyanate and organoselenocyanate compounds are of paramount importance in organic chemistry as they are key intermediates to access sulfur‐ and selenium‐containing compounds. Therefore, among the different synthetic pathways to get SCN‐ and SeCN‐containing molecules, original methodologies using electrophilic reagents have recently been explored. This Minireview will showcase the recent advances that have been made. In particular, the design of several electrophilic sources and their applications for the thiocyanation and the selenocyanation of various classes of compounds will be highlighted and discussed.
“…1 In addition, it is the product of the reaction of thiocyanogen with isobutylene. 2 Recent literature has shown the anti-inflammatory action of MAITC through (i) the irreversible inhibition of the macrophage migration inhibitory factor 3 and (ii) the inhibition of the caspase-1 activity through the inhibition of intracellular calcium levels. 4 Polymerized MAITC is used to obtain oral care compositions comprising a polymeric dye.…”
This feature focuses on a reagent chosen by a postgraduate, highlighting the uses and preparation of the reagent in current research spotlight
Methallyl Isothiocyanate
Compiled by Maksym FizerMaksym Fizer was born in Ukraine, in 1987. He obtained his B.Sc. in chemistry and his M.Sc. in organic chemistry ( 2009) from the Uzhgorod National University, Ukraine. He is currently working towards his Ph.D. under the supervision of Dr. Mikhail Slivka at the same institution. His research interest focusses on studying the synthesis of alkenyl-substituted bisthioureas, their alkaline cyclization into alkenylaminotriazolthiones, and their biological action.
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