Nucleophilic displacement of the nitro-group from nitroalkanes

Benn, M. H.; Meesters, A. C. M.

doi:10.1039/c39770000597

Cited by 6 publications

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“…In cases where direct comparison is possible, the recovered values are in good agreement with β nuc values reported for thiol attack on various electrophiles. 6c, We do note that, for CDNB and EPNP, the values obtained here are modestly higher than reported reactions with aliphatic thiols; this is likely a result of using arylthiols rather than alkanethiols and from inclusion of the hydrophobic solvent as observed for other electrophiles (and vide infra). Also, it should be noted that thiolate reactions with unbranched nitroalkanes proceed via a S N 2 nucleophilic mechanism, whereas α-substituted nitroalkanes may proceed by a radical-anion chain mechanism, S RN 1 mechanism. , Indeed, multiple mechanisms may be operative with GST catalysis. Obviously, our results are relevant only for nitroalkanes that react via a nucleophilic, S N 2 mechanism.…”

Section: Resultsmentioning

confidence: 99%

Contribution of Linear Free Energy Relationships to Isozyme- and pH-Dependent Substrate Selectivity of Glutathione S-Transferases: Comparison of Model Studies and Enzymatic Reactions

Nieslanik

Atkins

1998

J. Am. Chem. Soc.

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A novel application of linear free energy relationships is described in which the substrate selectivities and pH dependencies of glutathione S-transferases (GSTs) are correlated to the pK a of glutathione (GSH) at the active site. To determine whether the variation in the thiol pK a of GSH at the active sites of GST isozymes can contribute to their differential selectivity for electrophilic substrates, model studies were performed with 4-substituted thiobenzenes, with pK a values ranging from 4.5 to 7.5. Second-order rate constants were determined for the specific base-catalyzed reaction of each thiol with a diverse range of GST electrophilic substrates. Brønsted coefficients (βnuc) for these reactions in 10% DMF:90% H2O were determined for each electrophile; βnuc ranged from 0.16 to 0.93. In 30% DMF:70% H2O, the βnuc values increased relative to 10% DMF and ranged from 0.29 to 1.04. Numerical simulations demonstrate that these ranges of βnuc values along with the isozyme-dependent variation in GSH pK a could account for a 7.5-fold difference in relative turnover rates for GST catalysis of some electrophilic substrates. To challenge the predictions of this Brønsted analysis, electrophiles for which chemical steps are rate limiting in enzyme turnover were used as a substrate in reactions with a series of GSTA1-1 mutants with variable GSH pK a. βnuc values were determined to be 0.16 ± 0.05 for cumene hydroperoxide (CHP) and 0.25 ± 0.06 for 1-chloro-2,4-dinitrobenzene, in excellent agreement with the model studies. Furthermore, the dependence of the relative rates of CHP turnover on GSH pK a was well correlated, at pH 6.5, 7.4, and 8.0 with the relative rates predicted by the Brønsted analysis. Thus, even for a reaction characterized by a low βnuc value, variation of the pK a of enzyme-bound GSH leads to changes in the intrinsic reactivity of the nucleophilic GS-, according to the Brønsted free energy relationship. In principle, variation of the pK a of GSH may contribute to isozyme-dependent substrate selectivity.

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Section: Resultsmentioning

confidence: 99%

Contribution of Linear Free Energy Relationships to Isozyme- and pH-Dependent Substrate Selectivity of Glutathione S-Transferases: Comparison of Model Studies and Enzymatic Reactions

Nieslanik

Atkins

1998

J. Am. Chem. Soc.

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“…Thus, Me 3 S + OH - [28], Me 3 S=O + X - [29,30], Me 3 Se + OH - [31], (MeO) 2 CO [32][33][34], or MeNO 2 [35] can all be used as electrophilic methylating reagents. Thus, Me 3 S + OH - [28], Me 3 S=O + X - [29,30], Me 3 Se + OH - [31], (MeO) 2 CO [32][33][34], or MeNO 2 [35] can all be used as electrophilic methylating reagents.…”

Section: Good and Poor Leaving Groupsmentioning

confidence: 99%

Aliphatic Nucleophilic Substitutions: Problematic Electrophiles

Dörwald

2004

Side Reactions in Organic Synthesis

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Nucleophilic substitutions at sp 3 -hybridized carbon are among the most useful synthetic transformations, and have been thoroughly investigated [1][2][3]. The success of these reactions depends mainly on the structures of the nucleophile and electrophile, their concentration, and on the solvent and reaction temperature chosen. The structure of the electrophile in nucleophilic substitutions is of critical importance, because many unwanted side reactions result from unexpected reactivity of the electrophile.In Scheme 4.1 the mechanisms of typical monomolecular (Sn1) and bimolecular (Sn2) nucleophilic substitutions at a neutral electrophile with an anionic nucleophile are sketched. Sn1 reactions usually occur when the electrophile is sterically

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ChemInform Abstract: NUCLEOPHILIC DISPLACEMENT OF THE NITRO‐GROUP FROM NITROALKENES

Benn¹,

Meesters²

1978

Chemischer Informationsdienst

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Nucleophilic displacement of the nitro-group from nitroalkanes

Abstract: Reaction of toluene-9-thiolate anion, with primary or secondary, but not tertiary, nitroalkanes yields among other products the corresponding alkyl p-tolyl sulphides, apparently by a conventional SN2 displacement of the nitro-group.

Cited by 6 publications

References 0 publications

Contribution of Linear Free Energy Relationships to Isozyme- and pH-Dependent Substrate Selectivity of Glutathione S-Transferases: Comparison of Model Studies and Enzymatic Reactions

Contribution of Linear Free Energy Relationships to Isozyme- and pH-Dependent Substrate Selectivity of Glutathione S-Transferases: Comparison of Model Studies and Enzymatic Reactions

Aliphatic Nucleophilic Substitutions: Problematic Electrophiles

ChemInform Abstract: NUCLEOPHILIC DISPLACEMENT OF THE NITRO‐GROUP FROM NITROALKENES

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