Electrophilic and nucleophilic catalysis of the scission of the sulfur-sulfur bond

Kice, John L.

doi:10.1021/ar50002a004

Cited by 86 publications

(54 citation statements)

References 19 publications

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“…17a The same workers reported an order in thiophilicities of the halide ions, Cl À , Br À , I À as 1:3:87. Similar ordering in the thiophilicities of halide ions have been listed by Kice 31 for catalyses of reactions of nucleophiles at sulfenyl and sulfynyl sulfur atoms. In analogy with such cases we might expect in our reactions that iodide would give much more Th and halogen than bromide ion in reactions with 1.…”

Section: Reactions With Brsupporting

confidence: 66%

Reactions of nucleophiles with 5-(alkoxy)thianthrenium ions

Liu

Shine

Zhao

1999

J. Phys. Org. Chem.

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Reactions of 5-(alkoxy)thianthrenium perchlorates (1) with weakly basic nucleophiles Br À , IÀ and PhS À (X À ) in MeCN and DMSO led to S N 2 substitution, E2C elimination, and reaction at sulfonium sulfur to extents depending on the structure of the alkoxy group (RO) in 1 and the nucleophile. Three types of reaction occurred with R = cyclopentyl (1a), cyclohexyl (1b), cis-(1c) and trans-4-methylcyclohexyl (1d) and cycloheptyl (1e), and X À = Br À and I À . That is, S N 2 reaction gave RX and thianthrene 5-oxide (ThO), E2C reaction gave cycloalkene and ThO and reaction at sulfonium sulfur gave X 2 , thianthrene (Th) and cycloalkanol (ROH). Earlier work with R = Me (1f) and Et (1g) and X À = I À , Br À had shown that only S N 2 reaction occurred. In contrast with reactions of halide ions, reactions of PhS À with 1b-g occurred only at sulfonium sulfur, giving Th, ROH and PhSSPh (DPDS). For comparison with 1, reactions of Ph 2 S OMe (2) with I À and PhS À were carried out. Reaction with I À gave only Ph 2 S=O and MeI (S N 2). Reaction with PhS À gave very little PhSMe (S N 2) but mainly Ph 2 S, MeOH, and DPDS from reaction at sulfonium sulfur. The differences in nucleophilic pathways (PhS À vs Br À and I À ) in reactions with 1 and 2 are attributed to differences in thiophilicities of the nucleophiles. The thiophilicity of PhS À dominates its reactions with 1 and 2. The direction toward products (Th, ROH and DPDS) in these reactions is compounded by the ease of displacement of alkoxide from 1 and 2 by PhS À , and the ease with which, subsequently, thiophilic PhS À attacks sulfenyl sulfur in the resulting phenylthiosulfonium ion.

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Section: Reactions With Brsupporting

confidence: 66%

Reactions of nucleophiles with 5-(alkoxy)thianthrenium ions

Liu

Shine

Zhao

1999

J. Phys. Org. Chem.

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“…In most cases, these leaving groups are also sulfur-based, as in pyridyl disulfides (PDS), 2-nitrophenyl disulfides, methoxycarbonyl disulfides, [32] methane thiosulfonates (MTS), or thiosulfates (Bunte salts). [33] In the case of pyridyl-, 2-nitrophenyl-, and methoxycarbonyl disulfides, the reaction with a thiol(ate) is a disulfide exchange. MTS and thiosulfates produce methane sulfinic acid and sulfites, respectively, as leaving groups.…”

Section: Substitution At Sulfurmentioning

confidence: 99%

RAFT Polymerization and Thiol Chemistry: A Complementary Pairing for Implementing Modern Macromolecular Design

Roth

Boyer

Lowe

et al. 2011

Macromol. Rapid Commun.

185

146

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Reversible addition fragmentation chain transfer (RAFT) polymerization is one of the most extensively studied reversible deactivation radical polymerization methods for the production of well-defined polymers. After polymerization, the RAFT agent end-group can easily be converted into a thiol, opening manifold opportunities for thiol modification reactions. This review is focused both on the introduction of functional end-groups using well-established methods, such as thiol-ene chemistry, as well as on creating bio-cleavable disulfide linkages via disulfide exchange reactions. We demonstrate that thiol modification is a highly attractive and efficient chemistry for modifying RAFT polymers.

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“…The isolation of this tetrahedral intermediate led Jordan's group to postulate the presence of a proton donor in E1, which facilitates the disulfide bond scission of lipoic acid by electrophilic catalysis at the S6 atom (7,22). The E1b structure of Pseudomonas BCKD complex recently showed the presence of two histidine residues (His 312 -␣ and His 131 -␤Ј) flanking the cofactor ThDP in the active-site channel (2).…”

Section: Discussionmentioning

confidence: 99%

Roles of His291-α and His146-β′ in the Reductive Acylation Reaction Catalyzed by Human Branched-chain α-Ketoacid Dehydrogenase

Wynn

Machius²,

Chuang³

et al. 2003

Journal of Biological Chemistry

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We report here that alterations of either His 291 -␣ or His 146 -␤ in the active site of human branched-chain ␣-ketoacid dehydrogenase (E1b) impede both the decarboxylation and the reductive acylation reactions catalyzed by E1b as well as the binding of cofactor thiamin diphosphate (ThDP). In a refined human E1b active-site structure, His 291 -␣, which aligns with His 407 in Escherichia coli pyruvate dehydrogenase and His 263 in yeast transketolase, is on a largely ordered phosphorylation loop. The imidazole ring of His 291 -␣ in E1b coordinates to the terminal phosphate oxygen atoms of bound ThDP. The N3 atom of wild-type His 146 -␤ , which can be protonated, binds a water molecule and points toward the aminopyrimidine ring of ThDP. Remarkably, the H291A-␣ mutation results in a complete order-to-disorder transition of the loop region, which precludes the binding of the substrate lipoyl-bearing domain to E1b. The H146A-␤ mutation, on the other hand, does not alter the loop structure, but nullifies the reductive acylation activity of E1b. Our results suggest that: 1) His 291 -␣ plays a structural rather than a catalytic role in the binding of cofactor ThDP and the lipoyl-bearing domain to E1b, and 2) His 146 -␤ is an essential catalytic residue, probably functioning as a proton donor in the reductive acylation of lipoamide on the lipoyl-bearing domain.The mammalian branched-chain ␣-ketoacid dehydrogenase (BCKD) 1 complex catalyzes the oxidative decarboxylation of branched-chain ␣-ketoacids (Reaction 1) derived from transamination of leucine, isoleucine, and valine (1).The BCKD complex is a member of the highly conserved mitochondrial ␣-ketoacid dehydrogenase multienzyme complexes. This metabolic machine of 4 ϫ 10 6 daltons in size is organized around a 24-mer dihydrolipoyl transacylase (E2b) core, to which multiple copies of branched-chain ␣-ketoacid dehydrogenase (E1b), dihydrolipoamide dehydrogenase (E3), BCKD kinase, and BCKD phosphatase bind. In patients with heritable maple syrup urine disease, activity of the BCKD complex is deficient, resulting in often fatal acidosis, neurological disorders, and mental retardation (1).The E1b component is a thiamin diphosphate (ThDP)-dependent enzyme consisting of two ␣ (M r ϭ 45,500) and two ␤ (M r ϭ 37,500) subunits. The heterotetramer catalyzes both the ThDP-mediated decarboxylation of the ␣-ketoacids (Reaction 2) and the reductive acylation of the lipoyl moiety covalently attached to the ␤-hairpin tip of the lipoic acid-bearing domain (LBD) on the E2b subunit (Reaction 3).Crystal structures of Pseudomonas E1b (2) and human E1b (3) have been determined. These E1b proteins are heterotetramers each containing two ␣-and two ␤-subunits that form two ThDP-binding pockets at the ␣/␤Ј and the ␣Ј/␤ interfaces. This topology is conserved between E1b proteins and the homodimeric yeast transketolase; in the latter two ThDP-binding sites are formed at head-to-tail interfaces between two identical subunits (4), each corresponding to a fused ␣ and ␤ or ␣Ј and ␤Ј subunits of E1b. Res...

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Electrophilic and nucleophilic catalysis of the scission of the sulfur-sulfur bond

Cited by 86 publications

References 19 publications

Reactions of nucleophiles with 5-(alkoxy)thianthrenium ions

Reactions of nucleophiles with 5-(alkoxy)thianthrenium ions

RAFT Polymerization and Thiol Chemistry: A Complementary Pairing for Implementing Modern Macromolecular Design

Roles of His291-α and His146-β′ in the Reductive Acylation Reaction Catalyzed by Human Branched-chain α-Ketoacid Dehydrogenase

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