Activation energies for pyramidal inversion of sulfonium selenonium and telluronium ylides based on ab initio MO calculations

Shimizu, Toshio; Matsuhisa, Ayumi; Kamigata, Nobumasa; Ikuta, Shigeru

doi:10.1039/p29950001805

Cited by 24 publications

(13 citation statements)

References 12 publications

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“…A pyramidal inversion mechanism for the racemization of many telluronium species has been ruled out by theoretical studies at least at room temperature. [12,13] The first mechanism is as follows. The counteranion attacks the positive tellurium atom of the telluronium salt to give a tellurane, which yields achiral methyl phenyl telluride and benzyl halide by the ligand-coupling reaction, then the telluronium salt is reproduced.…”

Section: Configurational Stability and Racemization Mechanism Of Optimentioning

confidence: 99%

Isolation and Racemization Mechanism of Optically Active Benzylmethylphenyltelluronium Salts

et al. 2010

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Diastereomeric benzylmethylphenyltelluronium (1S)‐(+)‐ and (1R)‐(–)‐camphor‐10‐sulfonates were synthesized and resolved by fractional recrystallization. The absolute configurations of the isomers were determined by X‐ray crystallographic analysis. Enantiomerically pure telluronium salts with achiral counteranions, such as tetrafluoroborate, 4‐chlorobenzenesulfonate, bromide, iodide, and tetraphenylborate, were also obtained by anion‐exchange reactions of the separated diastereomers. The optically active telluronium salts possessing counteranions with a high nucleophilicity, such as bromide and iodide, were found to racemize in solution. The racemization of the telluronium salts was found to proceed either through the formation of a tellurane by the nucleophilic addition of a counteranion to the tellurium atom followed by decomposition into methyl phenyl telluride and benzyl halide or by several pseudorotations of the tellurane.

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Section: Configurational Stability and Racemization Mechanism Of Optimentioning

confidence: 99%

Isolation and Racemization Mechanism of Optically Active Benzylmethylphenyltelluronium Salts

et al. 2010

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“…The major difference between compounds 8 ‐ 9 and 15 is the stereochemistry at the sulfonium center. In contrast with the nitrogen analogs, the sulfonium containing compounds cannot invert easily since they have a high inversion barrier 28. Thus, it would appear that the configuration of the sulfonium‐ion is critical for activity and the design of new agents should take this into account.…”

Section: Introductionmentioning

confidence: 99%

Binding of sulfonium‐ion analogues of di‐epi‐swainsonine and 8‐epi‐lentiginosine to Drosophila Golgi α‐mannosidase II: The role of water in inhibitor binding

et al. 2007

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Retaining glycosidases operate by a two-step catalytic mechanism in which the transition states are characterized by buildup of a partial positive charge at the anomeric center. Sulfonium-ion analogues of the naturally occurring glycosidase inhibitors, swainsonine and 8-epi-lentiginosine, in which the bridgehead nitrogen atom is replaced by a sulfonium-ion, were synthesized in order to test the hypothesis that a sulfonium salt carrying a permanent positive charge would be an effective glycosidase inhibitor. Initial prediction based on computational docking indicated three plausible binding modes to Drosophila Golgi alpha-mannosidase II (dGMII), the most likely being close to that of swainsonine. Observation of the binding of di-epi-thioswainsonine and 8-epi-thiolentiginosine to dGMII from crystallographic data, however, revealed an orientation different from swainsonine in the active site. Screening these two compounds against dGMII shows that they are inhibitors with IC(50) values of 2.0 and 0.014 mM, respectively. This dramatic difference in affinity between the two compounds, which differ by only one hydroxyl group, is rationalized in terms of bound water molecules and the water molecule substructure in the active site, as identified by comparison of high resolution X-ray crystal structures of several dGMII-inhibitor complexes.

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“…Recently, we reported a theoretical study on the pyramidal inversion reaction of sulfonium, selenonium and telluronium ylides. 16 We also attempted to calculate the activation energies for the pyramidal inversion reaction of sulfonium, selenonium and telluronium imides by using ab initio MO calculations. In † A list of cartesian coordinates for the optimized geometries of chalcogen-onium imides at the local minima and the saddle-points for pyramidal inversion and chalcogen-nitrogen rotation modes is available as supplementary data available from BLDSC (SUPPL.…”

Section: Introductionmentioning

confidence: 99%

Pyramidal inversion energies and conformational analysis of chalcogen-onium imides based on ab initio MO calculations †

Shimizu¹,

Kamigata²,

Ikuta³

1999

J. Chem. Soc., Perkin Trans. 2

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Activation energies for pyramidal inversion of sulfonium selenonium and telluronium ylides based on ab initio MO calculations

Cited by 24 publications

References 12 publications

Isolation and Racemization Mechanism of Optically Active Benzylmethylphenyltelluronium Salts

Isolation and Racemization Mechanism of Optically Active Benzylmethylphenyltelluronium Salts

Binding of sulfonium‐ion analogues of di‐epi‐swainsonine and 8‐epi‐lentiginosine to Drosophila Golgi α‐mannosidase II: The role of water in inhibitor binding

Pyramidal inversion energies and conformational analysis of chalcogen-onium imides based on ab initio MO calculations †

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